Sections 3.1–3.2 Exponential and Logarithmic Functions V63.0121.021, Calculus I New York University October 21, 2010 Announcements I Midterm is graded and scores are on blackboard. Should get it back in recitation. I There is WebAssign due Monday/Tuesday next week. . . . . . .
105
Embed
Lesson 13: Exponential and Logarithmic Functions (Section 021 slides)
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
Sections 3.1–3.2Exponential and Logarithmic Functions
V63.0121.021, Calculus I
New York University
October 21, 2010
Announcements
I Midterm is graded and scores are on blackboard. Should get itback in recitation.
I There is WebAssign due Monday/Tuesday next week.
. . . . . .
. . . . . .
Announcements
I Midterm is graded andscores are on blackboard.Should get it back inrecitation.
I There is WebAssign dueMonday/Tuesday nextweek.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 2 / 38
. . . . . .
Midterm Statistics
I Average: 78.77%I Median: 80%I Standard Deviation: 12.39%I “good” is anything above average and “great” is anything more
than one standard deviation above average.I More than one SD below the mean is cause for concern.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 3 / 38
. . . . . .
Objectives for Sections 3.1 and 3.2
I Know the definition of anexponential function
I Know the properties ofexponential functions
I Understand and apply thelaws of logarithms,including the change ofbase formula.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 4 / 38
. . . . . .
Outline
Definition of exponential functions
Properties of exponential Functions
The number e and the natural exponential functionCompound InterestThe number eA limit
Logarithmic Functions
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 5 / 38
. . . . . .
Derivation of exponential functions
DefinitionIf a is a real number and n is a positive whole number, then
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 14 / 38
. . . . . .
Outline
Definition of exponential functions
Properties of exponential Functions
The number e and the natural exponential functionCompound InterestThe number eA limit
Logarithmic Functions
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 15 / 38
. . . . . .
Properties of exponential Functions.
.
TheoremIf a > 0 and a ̸= 1, then f(x) = ax is a continuous function with domain(−∞,∞) and range (0,∞). In particular, ax > 0 for all x. For any real numbersx and y, and positive numbers a and b we have
I ax+y = axay
I ax−y =ax
ay
(negative exponents mean reciprocals)
I (ax)y = axy
(fractional exponents mean roots)
I (ab)x = axbx
Proof.
I This is true for positive integer exponents by natural definitionI Our conventional definitions make these true for rational exponentsI Our limit definition make these for irrational exponents, too
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 16 / 38
. . . . . .
Properties of exponential Functions.
.
TheoremIf a > 0 and a ̸= 1, then f(x) = ax is a continuous function with domain(−∞,∞) and range (0,∞). In particular, ax > 0 for all x. For any real numbersx and y, and positive numbers a and b we have
I ax+y = axay
I ax−y =ax
ay (negative exponents mean reciprocals)I (ax)y = axy
(fractional exponents mean roots)
I (ab)x = axbx
Proof.
I This is true for positive integer exponents by natural definitionI Our conventional definitions make these true for rational exponentsI Our limit definition make these for irrational exponents, too
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 16 / 38
. . . . . .
Properties of exponential Functions.
.
TheoremIf a > 0 and a ̸= 1, then f(x) = ax is a continuous function with domain(−∞,∞) and range (0,∞). In particular, ax > 0 for all x. For any real numbersx and y, and positive numbers a and b we have
I ax+y = axay
I ax−y =ax
ay (negative exponents mean reciprocals)I (ax)y = axy (fractional exponents mean roots)I (ab)x = axbx
Proof.
I This is true for positive integer exponents by natural definitionI Our conventional definitions make these true for rational exponentsI Our limit definition make these for irrational exponents, too
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 16 / 38
. . . . . .
Simplifying exponential expressions
Example
Simplify: 82/3
Solution
I 82/3 =3√82 =
3√64 = 4
I Or,(
3√8)2
= 22 = 4.
Example
Simplify:√8
21/2
Answer2
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 17 / 38
. . . . . .
Simplifying exponential expressions
Example
Simplify: 82/3
Solution
I 82/3 =3√82 =
3√64 = 4
I Or,(
3√8)2
= 22 = 4.
Example
Simplify:√8
21/2
Answer2
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 17 / 38
. . . . . .
Simplifying exponential expressions
Example
Simplify: 82/3
Solution
I 82/3 =3√82 =
3√64 = 4
I Or,(
3√8)2
= 22 = 4.
Example
Simplify:√8
21/2
Answer2
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 17 / 38
. . . . . .
Simplifying exponential expressions
Example
Simplify: 82/3
Solution
I 82/3 =3√82 =
3√64 = 4
I Or,(
3√8)2
= 22 = 4.
Example
Simplify:√8
21/2
Answer2
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 17 / 38
. . . . . .
Simplifying exponential expressions
Example
Simplify: 82/3
Solution
I 82/3 =3√82 =
3√64 = 4
I Or,(
3√8)2
= 22 = 4.
Example
Simplify:√8
21/2
Answer2V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 17 / 38
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 26 / 38
. . . . . .
Meet the Mathematician: Leonhard Euler
I Born in Switzerland, livedin Prussia (Germany) andRussia
I Eyesight trouble all his life,blind from 1766 onward
I Hundreds of contributionsto calculus, number theory,graph theory, fluidmechanics, optics, andastronomy
Leonhard Paul EulerSwiss, 1707–1783
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 27 / 38
. . . . . .
A limit.
.
Question
What is limh→0
eh − 1h
?
Answer
I e = limn→∞
(1+ 1/n)n = limh→0
(1+ h)1/h. So for a small h, e ≈ (1+ h)1/h. So
eh − 1h
≈[(1+ h)1/h
]h − 1h
= 1
I It follows that limh→0
eh − 1h
= 1.
I This can be used to characterize e: limh→0
2h − 1h
= 0.693 · · · < 1 and
limh→0
3h − 1h
= 1.099 · · · > 1
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 28 / 38
. . . . . .
A limit.
.
Question
What is limh→0
eh − 1h
?
Answer
I e = limn→∞
(1+ 1/n)n = limh→0
(1+ h)1/h. So for a small h, e ≈ (1+ h)1/h. So
eh − 1h
≈[(1+ h)1/h
]h − 1h
= 1
I It follows that limh→0
eh − 1h
= 1.
I This can be used to characterize e: limh→0
2h − 1h
= 0.693 · · · < 1 and
limh→0
3h − 1h
= 1.099 · · · > 1
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 28 / 38
. . . . . .
A limit.
.
Question
What is limh→0
eh − 1h
?
Answer
I e = limn→∞
(1+ 1/n)n = limh→0
(1+ h)1/h. So for a small h, e ≈ (1+ h)1/h. So
eh − 1h
≈[(1+ h)1/h
]h − 1h
= 1
I It follows that limh→0
eh − 1h
= 1.
I This can be used to characterize e: limh→0
2h − 1h
= 0.693 · · · < 1 and
limh→0
3h − 1h
= 1.099 · · · > 1
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 28 / 38
. . . . . .
Outline
Definition of exponential functions
Properties of exponential Functions
The number e and the natural exponential functionCompound InterestThe number eA limit
Logarithmic Functions
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 29 / 38
. . . . . .
Logarithms
Definition
I The base a logarithm loga x is the inverse of the function ax
y = loga x ⇐⇒ x = ay
I The natural logarithm ln x is the inverse of ex. Soy = ln x ⇐⇒ x = ey.
Facts
(i) loga(x1 · x2) = loga x1 + loga x2
(ii) loga
(x1x2
)= loga x1 − loga x2
(iii) loga(xr) = r loga x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 30 / 38
. . . . . .
Logarithms
Definition
I The base a logarithm loga x is the inverse of the function ax
y = loga x ⇐⇒ x = ay
I The natural logarithm ln x is the inverse of ex. Soy = ln x ⇐⇒ x = ey.
Facts
(i) loga(x1 · x2) = loga x1 + loga x2
(ii) loga
(x1x2
)= loga x1 − loga x2
(iii) loga(xr) = r loga x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 30 / 38
. . . . . .
Logarithms
Definition
I The base a logarithm loga x is the inverse of the function ax
y = loga x ⇐⇒ x = ay
I The natural logarithm ln x is the inverse of ex. Soy = ln x ⇐⇒ x = ey.
Facts
(i) loga(x1 · x2) = loga x1 + loga x2
(ii) loga
(x1x2
)= loga x1 − loga x2
(iii) loga(xr) = r loga x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 30 / 38
. . . . . .
Logarithms
Definition
I The base a logarithm loga x is the inverse of the function ax
y = loga x ⇐⇒ x = ay
I The natural logarithm ln x is the inverse of ex. Soy = ln x ⇐⇒ x = ey.
Facts
(i) loga(x1 · x2) = loga x1 + loga x2
(ii) loga
(x1x2
)= loga x1 − loga x2
(iii) loga(xr) = r loga x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 30 / 38
. . . . . .
Logarithms convert products to sums
I Suppose y1 = loga x1 and y2 = loga x2I Then x1 = ay1 and x2 = ay2
I So x1x2 = ay1ay2 = ay1+y2
I Thereforeloga(x1 · x2) = loga x1 + loga x2
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 31 / 38
. . . . . .
Example
Write as a single logarithm: 2 ln 4− ln 3.
Solution
I 2 ln 4− ln 3 = ln 42 − ln 3 = ln42
3
I notln 42
ln 3!
Example
Write as a single logarithm: ln34+ 4 ln 2
Answerln 12
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 32 / 38
. . . . . .
Example
Write as a single logarithm: 2 ln 4− ln 3.
Solution
I 2 ln 4− ln 3 = ln 42 − ln 3 = ln42
3
I notln 42
ln 3!
Example
Write as a single logarithm: ln34+ 4 ln 2
Answerln 12
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 32 / 38
. . . . . .
Example
Write as a single logarithm: 2 ln 4− ln 3.
Solution
I 2 ln 4− ln 3 = ln 42 − ln 3 = ln42
3
I notln 42
ln 3!
Example
Write as a single logarithm: ln34+ 4 ln 2
Answerln 12
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 32 / 38
. . . . . .
Example
Write as a single logarithm: 2 ln 4− ln 3.
Solution
I 2 ln 4− ln 3 = ln 42 − ln 3 = ln42
3
I notln 42
ln 3!
Example
Write as a single logarithm: ln34+ 4 ln 2
Answerln 12
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 32 / 38
. . . . . .
Graphs of logarithmic functions
. .x
.y.y = 2x
.y = log2 x
. .(0,1)
..(1,0)
.y = 3x
.y = log3 x
.y = 10x
.y = log10 x
.y = ex
.y = ln x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 33 / 38
. . . . . .
Graphs of logarithmic functions
. .x
.y.y = 2x
.y = log2 x
. .(0,1)
..(1,0)
.y = 3x
.y = log3 x
.y = 10x
.y = log10 x
.y = ex
.y = ln x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 33 / 38
. . . . . .
Graphs of logarithmic functions
. .x
.y.y = 2x
.y = log2 x
. .(0,1)
..(1,0)
.y = 3x
.y = log3 x
.y = 10x
.y = log10 x
.y = ex
.y = ln x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 33 / 38
. . . . . .
Graphs of logarithmic functions
. .x
.y.y = 2x
.y = log2 x
. .(0,1)
..(1,0)
.y = 3x
.y = log3 x
.y = 10x
.y = log10 x
.y = ex
.y = ln x
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 33 / 38
. . . . . .
Change of base formula for exponentials
FactIf a > 0 and a ̸= 1, and the same for b, then
loga x =logb xlogb a
Proof.
I If y = loga x, then x = ay
I So logb x = logb(ay) = y logb a
I Thereforey = loga x =
logb xlogb a
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 34 / 38
. . . . . .
Change of base formula for exponentials
FactIf a > 0 and a ̸= 1, and the same for b, then
loga x =logb xlogb a
Proof.
I If y = loga x, then x = ay
I So logb x = logb(ay) = y logb a
I Thereforey = loga x =
logb xlogb a
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 34 / 38
. . . . . .
Example of changing base
Example
Find log2 8 by using log10 only.
Solution
log2 8 =log10 8log10 2
≈ 0.903090.30103
= 3
Surprised? No, log2 8 = log2 23 = 3 directly.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 35 / 38
. . . . . .
Example of changing base
Example
Find log2 8 by using log10 only.
Solution
log2 8 =log10 8log10 2
≈ 0.903090.30103
= 3
Surprised? No, log2 8 = log2 23 = 3 directly.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 35 / 38
. . . . . .
Example of changing base
Example
Find log2 8 by using log10 only.
Solution
log2 8 =log10 8log10 2
≈ 0.903090.30103
= 3
Surprised?
No, log2 8 = log2 23 = 3 directly.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 35 / 38
. . . . . .
Example of changing base
Example
Find log2 8 by using log10 only.
Solution
log2 8 =log10 8log10 2
≈ 0.903090.30103
= 3
Surprised? No, log2 8 = log2 23 = 3 directly.
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 35 / 38
. . . . . .
Upshot of changing base
The point of the change of base formula
loga x =logb xlogb a
=1
logb a· logb x = constant · logb x
is that all the logarithmic functions are multiples of each other. So justpick one and call it your favorite.
I Engineers like the common logarithm log = log10I Computer scientists like the binary logarithm lg = log2I Mathematicians like natural logarithm ln = loge
Naturally, we will follow the mathematicians. Just don’t pronounce it“lawn.”
V63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 36 / 38
. . . . . .
..“lawn”
.
.Image credit: SelvaV63.0121.021, Calculus I (NYU) Sections 3.1–3.2 Exponential Functions October 21, 2010 37 / 38