Real-World Example The Proof is in the Pudding · The Proof is in the Pudding Verify that the following are inverses. a) 𝑥= 6 𝑥−4 and 6 𝑥 +4 b) 𝑥=18 −3𝑥and 6 𝑥

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The Proof is in the Pudding Verify that the following are inverses.

a) 𝑓 𝑥 =6

𝑥−4and 𝑔 𝑥 =

6

𝑥+ 4

b) 𝑓 𝑥 = 18 − 3𝑥 and 𝑔 𝑥 = 6 −𝑥

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c) 𝑓 𝑥 = 𝑥2 + 10, 𝑥 ≥ 10; 𝑔 𝑥 = 𝑥 − 10

Real-World Example

Kendra earns $8 an hour, works at least 40 hours per week, and receives overtime pay at 1.5 times her regular hourly rate for any time over 40 hours . Her total earnings 𝑓(𝑥) for a week in which she worked 𝑥 hours is given by 𝑓 𝑥 =320 + 12 𝑥 − 40 .

a) Explain why the inverse exists. Then find the inverse

b) What do 𝑓−1 𝑥 and 𝑥 represent in the inverse function?

c) What restriction, if any, should be put on 𝑓 𝑥 and 𝑓−1 𝑥 . Explain

d) Find the number of hours Kendra worked last week if her earnings were $380.

Warm up Express the following in simplest form:

1. 7−1

2. 91

2

3. 82

3

4. 6−3

5. 16−3

4

Sketch the graph of f(x) and find the requested information

𝑓 𝑥 = 3𝑥

Domain:

Range:

y-intercept:

Asymptote:

End behavior:

Increasing:

Decreasing:

Sketch the graph of f(x) and find the requested information

𝑓 𝑥 = 2−𝑥

Domain:

Range:

y-intercept:

Asymptote:

End behavior:

Increasing:

Decreasing:

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Domain: Range:

y-intercept: x-intercept:

Extrema: Asymptote:

End behavior:

Continuity:

What is an exponential function?

Domain: Range:

y-intercept: x-intercept:

Extrema: Asymptote:

End behavior:

Continuity:

Transformations of exponential functions Using the rules we have already learned, describe the

following transformations given that 𝑓 𝑥 = 2𝑥 is the parent function.

a) 𝑔 𝑥 = 2𝑥+1

b) ℎ 𝑥 = 2−𝑥

c) 𝑗 𝑥 = −3(2𝑥)

d) 𝑘 𝑥 = 2𝑥 − 2

Natural Base exponential functionMost real world applications don’t use base 2 or base 10, but instead use an irrational number called e.

e is

𝑒 = lim𝑥→∞

1 +1

𝑥

𝑥

𝑓 𝑥 = 𝑒𝑥 is called the natural base exponential function.

Graphing the natural base exponential

Using a graphing calculator, graph:

a) 𝑓 𝑥 = 𝑒𝑥

b) a 𝑥 = 𝑒4𝑥

c) b 𝑥 = 𝑒−𝑥 + 3

d) 𝑐 𝑥 =1

2𝑒𝑥

Real world applications: compound interest Suppose an initial principle P is invested into an account with an

annual interest rate r, and the interest rate is compounded or reinvested annually. At the end of each year, the interest earned is added to the account balance. The sum is the new principle for the next year.

To allow for quarterly, monthly, or even daily compoundings, let n be the

The rate per compounding is:

The number of compoundings after t years is:

So the equation becomes:

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Krysti invests $300 in an account with a 6% interest rate, making no other deposits or withdrawals. What will Krysti’s account balance be after 20 years if the interest is compounded:

a) Semi-annually:

b) Monthly:

c) Daily:

Financial literacy: your turn1. If $10,000 is invested in an online savings account earning

8% per year, how much will be in the account at the end of10 years if there are no other deposits or withdrawals and interest is compounded:

a) Semiannually?

b) Quarterly?

c) Daily?

How does n affect account balance?Compounding n

𝑨 = 𝟑𝟎𝟎 𝟏 +𝟎. 𝟎𝟔

𝒏𝟐𝟎𝒏

Annually 1

Semiannually 2

Quarterly 4

Monthly 12

Daily 365

Hourly 8760

Continuous compound interest Suppose to compound continuously so that there is no

waiting period between interest payments.

𝐴 = 𝑃𝑒𝑟𝑡

Suppose Krysti finds an account that will allow her to invest her $300 at a 6% rate compounded continuously. If there are no other deposits or withdrawals, what will Krysti’s account balance be after 20 years?

If $10,000 is invested in an online savings account earning 8% per year compounded continuously, how much will be in the account at the end of 10 years if there are no other deposits or withdrawals?

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Exponential growth or decay Exponential growth and decay models apply to any situation where

growth is proportional to the initial size of the quantity being considered.

Rate r or k must be expressed as a decimal.

Mexico has a population of approximately 110 million. If Mexico’s population continues to grow at the described rate, predict the population of Mexico in 10 and 20 years.

a) 1.42% annually

b) 1.42% continuously

𝑁 = 𝑁0(1 + 𝑟)𝑡

𝑁 = 𝑁0𝑒𝑘𝑡

The population of a town is declining at a rate of 6%. If the current population is 12,426 people, predict the population in 5 and 1o years using each model.

a) Annually

b) Continuously

Exponential Modeling The table shows the number of reported cases of chicken pox in the US in 1980 and 2005.

a) If the number of reported cases of chicken pox is decreasing at an exponential rate, identify the rate of decline and write an exponential equation to model this situation

b) Use your model to predict when the number of cases will drop below 20,000.

Use the data in the table and assume that the population of Miami-Dade County is growing exponentially.

A. Identify the growth and write an exponential equation to model this growth.

B. Use your model to predict in which year the population of Miami-Dade County will surpass 2.7 million.

Through Word Problem p70 #44, 45, 56-58

Through Graphing p166 #2-10 Even

Through Transforming p166 #12-20 Even

Through Interest p166 #22-26 Even

Through Growth/Decay p166 #28-40 Even