Math 107

June27

Quiz5-Math108.docx

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MATH 107 QUIZ 5 2021

NAME: _______________________________

I have completed this assignment myself, working independently and not consulting anyone except the instructor.

INSTRUCTIONS

· The quiz is worth 100 points, and there is an extra credit opportunity at the end. There are 10 problems. This quiz is open book and open notes . This means that you may refer to your textbook, notes, and online classroom materials, but you must work independently and may not consult anyone (and confirm this with your submission). You may take as much time as you wish, provided you turn in your quiz no later than Tuesday, 11:59 PM.

· Show work/explanation where indicated. Answers without any work may earn little, if any, credit. You may type or write your work in your copy of the quiz, or if you prefer, create a document containing your work. Scanned work is acceptable also.

In your document, be sure to include your name and the assertion of independence of work.

· General quiz tips and instructions for submitting work are posted in the Quizzes module.

If you have any questions, please contact me by e-mail.

1. (8 pts)

(a) Let x = log 7 Find the X and State the exponential form of the equation .

(b) log 8 1 = _____ (fill in the blank)

Solution:

2. (10 pts) Let f (x) = 2x2 – 9 and g(x) = 3+2x

(a) Find the composite function and simplify the results. Show work.

Solution:

(b) Find . Show work.

Solution:

3. (6 pts) Based on data about the growth of a variety of ornamental trees, the following logarithmic model about these trees was determined:

h(t) = 6.108 ln(t) + 6.199, where t = age of tree in years and h (t) = height of tree, in feet.

(Note that "ln" refers to the natural log function) (explanation optional)

Using the model,

(a) At age 5 years, how tall is this type of ornamental cherry tree, to the nearest tenth of a foot?

Solution:

(b) At age 15 years, how tall is this type of ornamental cherry tree, to the nearest tenth of a foot?

Solution:

4. (8 pts) Solve the equation. Check all proposed solutions. Show work in solving and in checking, and state your final conclusion..

Solution:

The solution is

5 (10 pts)

a). Use composition of functions to show that the functions and

are inverse functions.

Hint: That is, carefully show that and show that .

Solution:

b). Rationalize the denominator:

Solution:

6. (15 pts) Let

(a) Find f 1 , the inverse function of f. Show work.

Solution:

(b) What is the domain of f (x)? What is the domain of the inverse function?

Solution:

(d) What is f 1 (…..), where the number in the blank is your answer from part (c)? work/explanation optional

7. (15 pts) Let f (x) = e – x + 3.

Answers can be stated without additional work/explanation.

(a) Which describes how the graph of f can be obtained from the graph of y = e x ? Choice: _______

A. Shift the graph of y = e x to the right by 1 unit and shift upward by 3 units.

B. Reflect the graph of y = e x across the y-axis and shift upward by 3 units

C. Reflect the graph of y = e x across the x-axis and shift upward by 3 units

D. Shift the graph of y = e x to the left by 1 unit and shift upward by 3 units.

(b) What is the horizontal asymptote?

(d) What is the range of f ?

(e) What is the y-intercept?

(f) Which is the graph of f ? Answer:______________

GRAPH A GRAPH B GRAPH C

expx+2 exp-x+2 exp-x+3

8. (3 pts) Convert to a logarithmic equation: (no explanation required) Answer: ______

NONLINEAR MODELS - For the latter part of the quiz, we will explore some nonlinear models.

9. (15 pts) QUADRATIC REGRESSION

Data: On a particular summer day, the outdoor temperature was recorded at 8 times of the day, and the following table was compiled. A scatterplot was produced and the parabola of best fit was determined.

t = Time of day (hour)	y = Outdoor Temperature (degrees F.)
7	52
9	67
11	73
13	76
14	78
17	79
20	76
23	61

Quadratic Polynomial of Best Fit:

y = 0.3476t2 + 10.948t 6.0778 where t = Time of day (hour) and y = Temperature (in degrees)

REMARKS: The times are the hours since midnight. For instance, 7 means 7 am, and 13 means 1 pm.

(a). Using algebraic techniques we have learned, find the maximum temperature predicted by the quadratic model and find the time when it occurred. Report the time to the nearest quarter hour (i.e., __:00 or __:15 or __:30 or __:45). (For instance, a time of 18.25 hours is reported as 6:15 pm.) Report the maximum temperature to the nearest tenth of a degree. Show algebraic work.

Solution:

(b). Use the quadratic polynomial to estimate the outdoor temperature at 7:30 am, to the nearest tenth of a degree. (work optional)

Solution:

(c) Use the quadratic polynomial y = 0.3476t2 + 10.948t 6.0778 together with algebra to estimate the time(s) of day when the outdoor temperature y was 72 degrees.

That is, solve the quadratic equation 72 = 0.3476t2 + 10.948t 6.0778 .

Show algebraic work in solving. State your results clearly; report the time(s) to the nearest quarter hour.

Solution:

10. (10 pts) + (extra credit at the end) EXPONENTIAL REGRESSION

Data: A cup of hot coffee was placed in a room maintained at a constant temperature of 69 degrees, and the coffee temperature was recorded periodically, in Table 1.

t = Time Elapsed (minutes)	C = Coffee Temperature (degrees F.)
0	166.0
10	140.5
20	125.2
30	110.3
40	104.5
50	98.4
60	93.9

TABLE 1

REMARKS:

Common sense tells us that the coffee will be cooling off and its temperature will decrease and approach the ambient temperature of the room, 69 degrees.

So, the temperature difference between the coffee temperature and the room temperature will decrease to 0.

We will fit the temperature difference data (Table 2) to an exponential curve of the form y = A ebt.

Notice that as t gets large, y will get closer and closer to 0, which is what the temperature difference will do.

So, we want to analyze the data where t = time elapsed and y = C 69, the temperature difference between the coffee temperature and the room temperature.

TABLE 2

t = Time Elapsed (minutes)	y = C 69 Temperature Difference (degrees F.)
0	97.0
10	71.5
20	56.2
30	41.3
40	35.5
50	29.4
60	24.9

Exponential Function of Best Fit (using the data in Table 2):

y = 89.976 e 0.023 t where t = Time Elapsed (minutes) and y = Temperature Difference (in degrees)

(a) Use the exponential function to estimate the temperature difference y when 25 minutes have elapsed. Report your estimated temperature difference to the nearest tenth of a degree. (explanation/work optional)

(b) Since y = C 69, we have coffee temperature C = y + 69. Take your difference estimate from part (a) and add 69 degrees. Interpret the result by filling in the blank:

When 25 minutes have elapsed, the estimated coffee temperature is ________ degrees.

(c) Suppose the coffee temperature C is 100 degrees. Then y = C 69 = ______ degrees is the temperature difference between the coffee and room temperatures.

(d) Consider the equation ____ = 89.976 e 0.023t where the ______ is filled in with your answer from part (c)

EXTRA CREDIT (6 pts):

Show algebraic work to solve this part (d) equation for t, to the nearest tenth. Interpret your results clearly in the context of the coffee application. [Use additional paper if needed]

The model estimates that it takes _____ minutes for the coffee to cool from ___ to ___ degrees room temperatures.

Don't forget to include your Last name into your quiz file name; otherwise, when I save it to grade, I would not know who this quiz belongs to, and will not grade it. Please follow this: your LastName Quiz5 Math107.

Temperature

on a Summer Day

y = -0.3476t2 + 10.948t - 6.0778 R² = 0.9699

7 9 11 13 14 17 20 23 52 67 73 76 78 79 76 61

Time of Day (hour)

Temperature (degrees)

Temperature Difference between Coffee and Room

y = 89.976e-0.023t R² = 0.9848

0 10 20 30 40 50 60 97 71.5 56.2 41.3 35.5 29.400000000000006 24.900000000000006

Time Elapsed (minutes)

Temperature Difference (degrees)

(

)

fxx

(

)

(

)

gxx

3245

(

)

72401

log2401

log24017

log2401

log72401

2401

212

-+=