Top Banner
. . SecƟon 4.1 Maximum and Minimum Values V63.0121.011: Calculus I Professor MaƩhew Leingang New York University April 4, 2011
95

Lesson 18: Maximum and Minimum Values (slides)

Dec 04, 2014

Download

Technology

There are various reasons why we would want to find the extreme (maximum and minimum values) of a function. Fermat's Theorem tells us we can find local extreme points by looking at critical points. This process is known as the Closed Interval Method.
Welcome message from author
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
Page 1: Lesson 18: Maximum and Minimum Values (slides)

..

Sec on 4.1Maximum and Minimum Values

V63.0121.011: Calculus IProfessor Ma hew Leingang

New York University

April 4, 2011

Page 2: Lesson 18: Maximum and Minimum Values (slides)

Announcements

I Quiz 4 on Sec ons 3.3, 3.4, 3.5,and 3.7 next week (April 14/15)

I Quiz 5 on Sec ons 4.1–4.4April 28/29

I Final Exam Monday May 12,2:00–3:50pm

Page 3: Lesson 18: Maximum and Minimum Values (slides)

ObjectivesI Understand and be able toexplain the statement of theExtreme Value Theorem.

I Understand and be able toexplain the statement ofFermat’s Theorem.

I Use the Closed Interval Methodto find the extreme values of afunc on defined on a closedinterval.

Page 4: Lesson 18: Maximum and Minimum Values (slides)

OutlineIntroduc on

The Extreme Value Theorem

Fermat’s Theorem (not the last one)Tangent: Fermat’s Last Theorem

The Closed Interval Method

Examples

Page 5: Lesson 18: Maximum and Minimum Values (slides)

..

Optimize

Page 6: Lesson 18: Maximum and Minimum Values (slides)

Why go to the extremes?I Ra onally speaking, it isadvantageous to find theextreme values of a func on(maximize profit, minimize costs,etc.)

I Many laws of science arederived from minimizingprinciples.

I Maupertuis’ principle: “Ac on isminimized through the wisdomof God.”

Pierre-Louis Maupertuis(1698–1759)

Page 7: Lesson 18: Maximum and Minimum Values (slides)

..

Design

Page 8: Lesson 18: Maximum and Minimum Values (slides)

Why go to the extremes?I Ra onally speaking, it isadvantageous to find theextreme values of a func on(maximize profit, minimize costs,etc.)

I Many laws of science arederived from minimizingprinciples.

I Maupertuis’ principle: “Ac on isminimized through the wisdomof God.”

Pierre-Louis Maupertuis(1698–1759)

Page 9: Lesson 18: Maximum and Minimum Values (slides)

..

Optics

Page 10: Lesson 18: Maximum and Minimum Values (slides)

Why go to the extremes?I Ra onally speaking, it isadvantageous to find theextreme values of a func on(maximize profit, minimize costs,etc.)

I Many laws of science arederived from minimizingprinciples.

I Maupertuis’ principle: “Ac on isminimized through the wisdomof God.”

Pierre-Louis Maupertuis(1698–1759)

Page 11: Lesson 18: Maximum and Minimum Values (slides)

OutlineIntroduc on

The Extreme Value Theorem

Fermat’s Theorem (not the last one)Tangent: Fermat’s Last Theorem

The Closed Interval Method

Examples

Page 12: Lesson 18: Maximum and Minimum Values (slides)

Extreme points and valuesDefini onLet f have domain D.

I The func on f has an absolute maximum(or global maximum) (respec vely,absolute minimum) at c if f(c) ≥ f(x)(respec vely, f(c) ≤ f(x)) for all x in D

I The number f(c) is called themaximumvalue (respec vely,minimum value) of fon D.

I An extremum is either a maximum or aminimum. An extreme value is either amaximum value or minimum value.

..

Image credit: Patrick Q

Page 13: Lesson 18: Maximum and Minimum Values (slides)

Extreme points and valuesDefini onLet f have domain D.

I The func on f has an absolute maximum(or global maximum) (respec vely,absolute minimum) at c if f(c) ≥ f(x)(respec vely, f(c) ≤ f(x)) for all x in D

I The number f(c) is called themaximumvalue (respec vely,minimum value) of fon D.

I An extremum is either a maximum or aminimum. An extreme value is either amaximum value or minimum value.

..

Image credit: Patrick Q

Page 14: Lesson 18: Maximum and Minimum Values (slides)

Extreme points and valuesDefini onLet f have domain D.

I The func on f has an absolute maximum(or global maximum) (respec vely,absolute minimum) at c if f(c) ≥ f(x)(respec vely, f(c) ≤ f(x)) for all x in D

I The number f(c) is called themaximumvalue (respec vely,minimum value) of fon D.

I An extremum is either a maximum or aminimum. An extreme value is either amaximum value or minimum value.

..

Image credit: Patrick Q

Page 15: Lesson 18: Maximum and Minimum Values (slides)

Extreme points and valuesDefini onLet f have domain D.

I The func on f has an absolute maximum(or global maximum) (respec vely,absolute minimum) at c if f(c) ≥ f(x)(respec vely, f(c) ≤ f(x)) for all x in D

I The number f(c) is called themaximumvalue (respec vely,minimum value) of fon D.

I An extremum is either a maximum or aminimum. An extreme value is either amaximum value or minimum value.

..

Image credit: Patrick Q

Page 16: Lesson 18: Maximum and Minimum Values (slides)

The Extreme Value TheoremTheorem (The Extreme ValueTheorem)

Let f be a func on which iscon nuous on the closedinterval [a, b]. Then f a ainsan absolute maximum valuef(c) and an absolute minimumvalue f(d) at numbers c and din [a, b].

.

Page 17: Lesson 18: Maximum and Minimum Values (slides)

The Extreme Value TheoremTheorem (The Extreme ValueTheorem)

Let f be a func on which iscon nuous on the closedinterval [a, b]. Then f a ainsan absolute maximum valuef(c) and an absolute minimumvalue f(d) at numbers c and din [a, b].

...a..

b..

Page 18: Lesson 18: Maximum and Minimum Values (slides)

The Extreme Value TheoremTheorem (The Extreme ValueTheorem)

Let f be a func on which iscon nuous on the closedinterval [a, b]. Then f a ainsan absolute maximum valuef(c) and an absolute minimumvalue f(d) at numbers c and din [a, b].

...a..

b...

cmaximum

.

maximumvaluef(c)

Page 19: Lesson 18: Maximum and Minimum Values (slides)

The Extreme Value TheoremTheorem (The Extreme ValueTheorem)

Let f be a func on which iscon nuous on the closedinterval [a, b]. Then f a ainsan absolute maximum valuef(c) and an absolute minimumvalue f(d) at numbers c and din [a, b].

...a..

b...

cmaximum

.

maximumvaluef(c)

..d

minimum

.

minimumvaluef(d)

Page 20: Lesson 18: Maximum and Minimum Values (slides)

No proof of EVT forthcoming

I This theorem is very hard to prove without using technical factsabout con nuous func ons and closed intervals.

I But we can show the importance of each of the hypotheses.

Page 21: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #1Example

Consider the func on

f(x) =

{x 0 ≤ x < 1x− 2 1 ≤ x ≤ 2.

.. |.1

....

Then although values of f(x) get arbitrarily close to 1 and neverbigger than 1, 1 is not the maximum value of f on [0, 1] because it isnever achieved. This does not violate EVT because f is notcon nuous.

Page 22: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #1Example

Consider the func on

f(x) =

{x 0 ≤ x < 1x− 2 1 ≤ x ≤ 2.

.. |.1

....

Then although values of f(x) get arbitrarily close to 1 and neverbigger than 1, 1 is not the maximum value of f on [0, 1] because it isnever achieved. This does not violate EVT because f is notcon nuous.

Page 23: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #1Example

Consider the func on

f(x) =

{x 0 ≤ x < 1x− 2 1 ≤ x ≤ 2.

.. |.1

....

Then although values of f(x) get arbitrarily close to 1 and neverbigger than 1, 1 is not the maximum value of f on [0, 1] because it isnever achieved.

This does not violate EVT because f is notcon nuous.

Page 24: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #1Example

Consider the func on

f(x) =

{x 0 ≤ x < 1x− 2 1 ≤ x ≤ 2.

.. |.1

....

Then although values of f(x) get arbitrarily close to 1 and neverbigger than 1, 1 is not the maximum value of f on [0, 1] because it isnever achieved. This does not violate EVT because f is notcon nuous.

Page 25: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #2Example

Consider the func on f(x) = x restricted to the interval [0, 1).

I There is s ll no maximumvalue (values getarbitrarily close to 1 butdo not achieve it).

I This does not violate EVTbecause the domain isnot closed.

.. |.1

..

Page 26: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #2Example

Consider the func on f(x) = x restricted to the interval [0, 1).

I There is s ll no maximumvalue (values getarbitrarily close to 1 butdo not achieve it).

I This does not violate EVTbecause the domain isnot closed.

.. |.1

..

Page 27: Lesson 18: Maximum and Minimum Values (slides)

Bad Example #2Example

Consider the func on f(x) = x restricted to the interval [0, 1).

I There is s ll no maximumvalue (values getarbitrarily close to 1 butdo not achieve it).

I This does not violate EVTbecause the domain isnot closed.

.. |.1

..

Page 28: Lesson 18: Maximum and Minimum Values (slides)

Final Bad ExampleExample

The func on f(x) =1xis con nuous on the closed interval [1,∞).

...1

.

There is no minimum value (values get arbitrarily close to 0 but donot achieve it). This does not violate EVT because the domain is notbounded.

Page 29: Lesson 18: Maximum and Minimum Values (slides)

Final Bad ExampleExample

The func on f(x) =1xis con nuous on the closed interval [1,∞).

...1

.

There is no minimum value (values get arbitrarily close to 0 but donot achieve it).

This does not violate EVT because the domain is notbounded.

Page 30: Lesson 18: Maximum and Minimum Values (slides)

Final Bad ExampleExample

The func on f(x) =1xis con nuous on the closed interval [1,∞).

...1

.

There is no minimum value (values get arbitrarily close to 0 but donot achieve it). This does not violate EVT because the domain is notbounded.

Page 31: Lesson 18: Maximum and Minimum Values (slides)

OutlineIntroduc on

The Extreme Value Theorem

Fermat’s Theorem (not the last one)Tangent: Fermat’s Last Theorem

The Closed Interval Method

Examples

Page 32: Lesson 18: Maximum and Minimum Values (slides)

Local extremaDefini on

I A func on f has a localmaximum or rela ve maximumat c if f(c) ≥ f(x) when x is nearc. This means that f(c) ≥ f(x)for all x in some open intervalcontaining c.

I Similarly, f has a local minimumat c if f(c) ≤ f(x) when x is nearc.

..|.a. |.

b..

Page 33: Lesson 18: Maximum and Minimum Values (slides)

Local extremaDefini on

I A func on f has a localmaximum or rela ve maximumat c if f(c) ≥ f(x) when x is nearc. This means that f(c) ≥ f(x)for all x in some open intervalcontaining c.

I Similarly, f has a local minimumat c if f(c) ≤ f(x) when x is nearc.

..|.a. |.

b....

localmaximum

Page 34: Lesson 18: Maximum and Minimum Values (slides)

Local extremaDefini on

I A func on f has a localmaximum or rela ve maximumat c if f(c) ≥ f(x) when x is nearc. This means that f(c) ≥ f(x)for all x in some open intervalcontaining c.

I Similarly, f has a local minimumat c if f(c) ≤ f(x) when x is nearc.

..|.a. |.

b....

localmaximum

..local

minimum

Page 35: Lesson 18: Maximum and Minimum Values (slides)

Local extremaI A local extremum could be aglobal extremum, but not ifthere are more extreme valueselsewhere.

I A global extremum could be alocal extremum, but not if it isan endpoint.

..|.a. |.

b....

localmaximum

..globalmax

.local andglobalmin

Page 36: Lesson 18: Maximum and Minimum Values (slides)

Fermat’s TheoremTheorem (Fermat’s Theorem)

Suppose f has alocal extremum at cand f isdifferen able at c.Then f′(c) = 0. ..|.

a. |.

b....local

maximum

..localminimum

Page 37: Lesson 18: Maximum and Minimum Values (slides)

Fermat’s TheoremTheorem (Fermat’s Theorem)

Suppose f has alocal extremum at cand f isdifferen able at c.Then f′(c) = 0. ..|.

a. |.

b....local

maximum

..localminimum

Page 38: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0 =⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0 =⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 39: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0

=⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0 =⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 40: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0 =⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0 =⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 41: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0 =⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0

=⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 42: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0 =⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0 =⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 43: Lesson 18: Maximum and Minimum Values (slides)

Proof of Fermat’s TheoremSuppose that f has a local maximum at c.

I If x is slightly greater than c, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≤ 0 =⇒ limx→c+

f(x)− f(c)x− c

≤ 0

I The same will be true on the other end: if x is slightly less thanc, f(x) ≤ f(c). This means

f(x)− f(c)x− c

≥ 0 =⇒ limx→c−

f(x)− f(c)x− c

≥ 0

I Since the limit f′(c) = limx→c

f(x)− f(c)x− c

exists, it must be 0.

Page 44: Lesson 18: Maximum and Minimum Values (slides)

Meet the Mathematician: Pierre de Fermat

I 1601–1665I Lawyer and numbertheorist

I Proved many theorems,didn’t quite prove his lastone

Page 45: Lesson 18: Maximum and Minimum Values (slides)

Tangent: Fermat’s Last TheoremI Plenty of solu ons to

x2 + y2 = z2 among posi vewhole numbers (e.g., x = 3,y = 4, z = 5)

I No solu ons to x3 + y3 = z3among posi ve whole numbers

I Fermat claimed no solu ons toxn + yn = zn but didn’t writedown his proof

I Not solved un l 1998!(Taylor–Wiles)

Page 46: Lesson 18: Maximum and Minimum Values (slides)

Tangent: Fermat’s Last TheoremI Plenty of solu ons to

x2 + y2 = z2 among posi vewhole numbers (e.g., x = 3,y = 4, z = 5)

I No solu ons to x3 + y3 = z3among posi ve whole numbers

I Fermat claimed no solu ons toxn + yn = zn but didn’t writedown his proof

I Not solved un l 1998!(Taylor–Wiles)

Page 47: Lesson 18: Maximum and Minimum Values (slides)

Tangent: Fermat’s Last TheoremI Plenty of solu ons to

x2 + y2 = z2 among posi vewhole numbers (e.g., x = 3,y = 4, z = 5)

I No solu ons to x3 + y3 = z3among posi ve whole numbers

I Fermat claimed no solu ons toxn + yn = zn but didn’t writedown his proof

I Not solved un l 1998!(Taylor–Wiles)

Page 48: Lesson 18: Maximum and Minimum Values (slides)

Tangent: Fermat’s Last TheoremI Plenty of solu ons to

x2 + y2 = z2 among posi vewhole numbers (e.g., x = 3,y = 4, z = 5)

I No solu ons to x3 + y3 = z3among posi ve whole numbers

I Fermat claimed no solu ons toxn + yn = zn but didn’t writedown his proof

I Not solved un l 1998!(Taylor–Wiles)

Page 49: Lesson 18: Maximum and Minimum Values (slides)

OutlineIntroduc on

The Extreme Value Theorem

Fermat’s Theorem (not the last one)Tangent: Fermat’s Last Theorem

The Closed Interval Method

Examples

Page 50: Lesson 18: Maximum and Minimum Values (slides)

Flowchart for placing extremaThanks to FermatSuppose f is acon nuousfunc on onthe closed,boundedinterval[a, b], and c isa globalmaximumpoint.

..start.

Is c anendpoint?

.

c = a orc = b

. c is alocal max

.

Is f diff’bleat c?

.

f is notdiff at c

.

f′(c) = 0

.

no

.

yes

.

no

.

yes

Page 51: Lesson 18: Maximum and Minimum Values (slides)

The Closed Interval Method

This means to find the maximum value of f on [a, b], we need to:I Evaluate f at the endpoints a and bI Evaluate f at the cri cal points or cri cal numbers x whereeither f′(x) = 0 or f is not differen able at x.

I The points with the largest func on value are the globalmaximum points

I The points with the smallest or most nega ve func on valueare the global minimum points.

Page 52: Lesson 18: Maximum and Minimum Values (slides)

OutlineIntroduc on

The Extreme Value Theorem

Fermat’s Theorem (not the last one)Tangent: Fermat’s Last Theorem

The Closed Interval Method

Examples

Page 53: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a linear functionExample

Find the extreme values of f(x) = 2x− 5 on [−1, 2].

Solu on

Since f′(x) = 2, which is neverzero, we have no cri cal pointsand we need only inves gatethe endpoints:

I f(−1) = 2(−1)− 5 = −7I f(2) = 2(2)− 5 = −1

SoI The absolute minimum

(point) is at−1; theminimum value is−7.

I The absolute maximum(point) is at 2; themaximum value is−1.

Page 54: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a linear functionExample

Find the extreme values of f(x) = 2x− 5 on [−1, 2].

Solu on

Since f′(x) = 2, which is neverzero, we have no cri cal pointsand we need only inves gatethe endpoints:

I f(−1) = 2(−1)− 5 = −7I f(2) = 2(2)− 5 = −1

SoI The absolute minimum

(point) is at−1; theminimum value is−7.

I The absolute maximum(point) is at 2; themaximum value is−1.

Page 55: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a linear functionExample

Find the extreme values of f(x) = 2x− 5 on [−1, 2].

Solu on

Since f′(x) = 2, which is neverzero, we have no cri cal pointsand we need only inves gatethe endpoints:

I f(−1) = 2(−1)− 5 = −7I f(2) = 2(2)− 5 = −1

SoI The absolute minimum

(point) is at−1; theminimum value is−7.

I The absolute maximum(point) is at 2; themaximum value is−1.

Page 56: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0.

So our points tocheck are:

I f(−1) =I f(0) =I f(2) =

Page 57: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0.

So our points tocheck are:

I f(−1) =I f(0) =I f(2) =

Page 58: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) =I f(0) =I f(2) =

Page 59: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) = 0I f(0) =I f(2) =

Page 60: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) = 0I f(0) = − 1I f(2) =

Page 61: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) = 0I f(0) = − 1I f(2) = 3

Page 62: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) = 0I f(0) = − 1 (absolute min)I f(2) = 3

Page 63: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a quadraticfunction

Example

Find the extreme values of f(x) = x2 − 1 on [−1, 2].

Solu onWe have f′(x) = 2x, which is zero when x = 0. So our points tocheck are:

I f(−1) = 0I f(0) = − 1 (absolute min)I f(2) = 3 (absolute max)

Page 64: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1.

The values to check are

I f(−1) =

− 4 (global min)

I f(0) =

1 (local max)

I f(1) =

0 (local min)

I f(2) =

5 (global max)

Page 65: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1.

The values to check are

I f(−1) =

− 4 (global min)

I f(0) =

1 (local max)

I f(1) =

0 (local min)

I f(2) =

5 (global max)

Page 66: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) =

− 4 (global min)

I f(0) =

1 (local max)

I f(1) =

0 (local min)

I f(2) =

5 (global max)

Page 67: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4

(global min)I f(0) =

1 (local max)

I f(1) =

0 (local min)

I f(2) =

5 (global max)

Page 68: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4

(global min)

I f(0) = 1

(local max)I f(1) =

0 (local min)

I f(2) =

5 (global max)

Page 69: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4

(global min)

I f(0) = 1

(local max)

I f(1) = 0

(local min)I f(2) =

5 (global max)

Page 70: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4

(global min)

I f(0) = 1

(local max)

I f(1) = 0

(local min)

I f(2) = 5

(global max)

Page 71: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4 (global min)I f(0) = 1

(local max)

I f(1) = 0

(local min)

I f(2) = 5

(global max)

Page 72: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4 (global min)I f(0) = 1

(local max)

I f(1) = 0

(local min)

I f(2) = 5 (global max)

Page 73: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4 (global min)I f(0) = 1 (local max)I f(1) = 0

(local min)

I f(2) = 5 (global max)

Page 74: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of a cubic functionExample

Find the extreme values of f(x) = 2x3 − 3x2 + 1 on [−1, 2].

Solu onSince f′(x) = 6x2 − 6x = 6x(x− 1), we have cri cal points at x = 0and x = 1. The values to check are

I f(−1) = − 4 (global min)I f(0) = 1 (local max)I f(1) = 0 (local min)I f(2) = 5 (global max)

Page 75: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

Page 76: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

Page 77: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3. Then

f′(x) =53x2/3 +

43x−1/3 =

13x−1/3(5x+ 4)

Page 78: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3. Then

f′(x) =53x2/3 +

43x−1/3 =

13x−1/3(5x+ 4)

Thus f′(−4/5) = 0 and f is not differen able at 0. Thus there are twocri cal points.

Page 79: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) =I f(−4/5) =

I f(0) =I f(2) =

Page 80: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) =

I f(0) =I f(2) =

Page 81: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341I f(0) =I f(2) =

Page 82: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341I f(0) = 0I f(2) =

Page 83: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341I f(0) = 0I f(2) = 6.3496

Page 84: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341I f(0) = 0 (absolute min)I f(2) = 6.3496

Page 85: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341I f(0) = 0 (absolute min)I f(2) = 6.3496 (absolute max)

Page 86: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of an algebraic functionExample

Find the extreme values of f(x) = x2/3(x+ 2) on [−1, 2].

Solu onWrite f(x) = x5/3 + 2x2/3.

I f(−1) = 1I f(−4/5) = 1.0341 (rela ve max)I f(0) = 0 (absolute min)I f(2) = 6.3496 (absolute max)

Page 87: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.)

So our points to check are:

I f(−2) =I f(0) =I f(1) =

Page 88: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.)

So our points to check are:

I f(−2) =I f(0) =I f(1) =

Page 89: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) =

I f(0) =I f(1) =

Page 90: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) = 0I f(0) =

I f(1) =

Page 91: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) = 0I f(0) = 2I f(1) =

Page 92: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) = 0I f(0) = 2I f(1) =

√3

Page 93: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) = 0 (absolute min)I f(0) = 2I f(1) =

√3

Page 94: Lesson 18: Maximum and Minimum Values (slides)

Extreme values of another algebraic function

Example

Find the extreme values of f(x) =√

4− x2 on [−2, 1].

Solu onWe have f′(x) = − x√

4− x2, which is zero when x = 0. (f is not

differen able at±2 as well.) So our points to check are:I f(−2) = 0 (absolute min)I f(0) = 2 (absolute max)I f(1) =

√3

Page 95: Lesson 18: Maximum and Minimum Values (slides)

Summary

I The Extreme Value Theorem: a con nuous func on on a closedinterval must achieve its max and min

I Fermat’s Theorem: local extrema are cri cal pointsI The Closed Interval Method: an algorithm for finding globalextrema

I Show your work unless you want to end up like Fermat!