Calculus AB : Applications of Integration

Study concepts, example questions & explanations for Calculus AB

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Example Questions

Example Question #3 : Find Average Value

Find the average value of the function \(\displaystyle f(x)=4e^{2x}\) over the interval \(\displaystyle [0,5]\)

Possible Answers:

\(\displaystyle e^5\)

\(\displaystyle \frac{2}{5}(e^{10}-1)\)

\(\displaystyle 2e^10\)

\(\displaystyle \frac{2}{5}(e^5-1)\)

Correct answer:

\(\displaystyle \frac{2}{5}(e^{10}-1)\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation is very helpful because it provides a simple way to determine the average value by substituting in values of the bounds and the function itself:

\(\displaystyle f_{avg}=\frac{1}{5-0}\int_{0}^{5}4e^{2x} dx=(\frac{1}{5})[4e^{2x} * \frac{1}{2}] |_0^5 =\frac{2}{5}e^{2(5)}-\frac{2}{5}e^{2(0)}=\frac{2}{5}(e^{10}-1)\)

Example Question #4 : Find Average Value

Find the average value of the function \(\displaystyle f(t)=4+2cos(2t)\) over the interval \(\displaystyle [0,\frac{\pi}{4}]\).

Possible Answers:

\(\displaystyle \frac{\pi}{4} + 2\)

\(\displaystyle 4+\frac{4}{\pi}\)

\(\displaystyle 1+\frac{4}{\pi}\)

\(\displaystyle 4-\frac{4}{\pi}\)

Correct answer:

\(\displaystyle 4+\frac{4}{\pi}\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function and interval to solve for the average value. While the function in this problem contains a trigonometric function, the same approach can be applied. Remember that the function is in terms of t, so the definite integral expression should likewise be in terms of \(\displaystyle t\).

\(\displaystyle f_{avg}=\frac{1}{\frac{\pi}{4}-0}\int_{0}^{\frac{\pi}{4}}4+2cos(2t) dt=(\frac{4}{\pi})[4t+sin(2t)] |_0^{\frac{\pi}{4}}\)\(\displaystyle =(\frac{4}{\pi})[\pi +1-0-0]=4+\frac{4}{\pi}\)

Example Question #5 : Find Average Value

Identify the correct integral expression for the average value of the function\(\displaystyle f(t)=6-3tsin(t^2)\) over the interval \(\displaystyle [0,\pi]\).

Possible Answers:

\(\displaystyle \frac{1}{\pi}\int_{0}^{\pi}6-3xsin(x^2) dt\)

\(\displaystyle \frac{1}{\pi}\int_{0}^{\pi}6-3tsin(t^2) dt\)

\(\displaystyle \int_{0}^{\pi}6-3tsin(t^2) dx\)

\(\displaystyle \int_{0}^{\pi}6-3tsin(t^2) dt\)

Correct answer:

\(\displaystyle \frac{1}{\pi}\int_{0}^{\pi}6-3tsin(t^2) dt\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function and interval to solve for the average value. While the function in this problem contains a trigonometric function, the same approach can be applied. Remember that the function is in terms of \(\displaystyle t\), so the definite integral expression should likewise be in terms of \(\displaystyle t\).

\(\displaystyle f_{avg}=\frac{1}{\pi-0}\int_{0}^{\pi}6-(3t)sin(t^2) dt =\frac{1}{\pi}\int_{0}^{\pi}6-3tsin(t^2) dt\)

Example Question #6 : Find Average Value

Find the average value of the function \(\displaystyle f(x)=2x^5-6x^3+7\) over the interval \(\displaystyle [1,2]\).

Possible Answers:

\(\displaystyle 7.5\)

\(\displaystyle 4\)

\(\displaystyle 5.5\)

\(\displaystyle 6\)

Correct answer:

\(\displaystyle 5.5\)

Explanation:

Because the objective of this problem is to find the average value of the function, the formula f\(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\) will be useful. Since the interval and function are provided, this problem consists of recognizing the base components and making the appropriate substitutions:

\(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx=\frac{1}{2-1}\int_{1}^{2}2x^5-6x^3+7 dx =[\frac{1}{3}x^6-\frac{3}{2}x^4+7x] |_1^2\)\(\displaystyle =\frac{64}{3}-24+14-\frac{1}{3}+\frac{3}{2}-7=5.5\)

Example Question #7 : Find Average Value

Identify the correct integral expression for the average value of the function \(\displaystyle f(x)=1x+2x\) over the interval \(\displaystyle [1,4]\).

Possible Answers:

\(\displaystyle \frac{1}{3}\int_{1}^{4}\frac{1}{t}+\sqrt{2t} dx\)

\(\displaystyle \frac{1}{3}\int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx\)

\(\displaystyle \int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx\)

\(\displaystyle \frac{1}{4}\int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx\)

Correct answer:

\(\displaystyle \frac{1}{3}\int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function and interval to solve for the average value. Because the function indicated in the problem is in terms of \(\displaystyle x\), the definite integral expression should also be in terms of \(\displaystyle x\).

\(\displaystyle f_{avg}=\frac{1}{4-1}\int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx =\frac{1}{3}\int_{1}^{4}\frac{1}{x}+\sqrt{2x} dx\)

Example Question #8 : Find Average Value

Find the average value of the function \(\displaystyle f(x)=20x+x^3\) over the interval \(\displaystyle [-1,1]\).

Possible Answers:

\(\displaystyle -1\)

\(\displaystyle 1\)

\(\displaystyle 2\)

\(\displaystyle 0\)

Correct answer:

\(\displaystyle 0\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function and interval to solve for the average value. Because the function indicated in the problem is in terms of \(\displaystyle x\), the definite integral expression should also be in terms of \(\displaystyle x\).

\(\displaystyle f_{avg}=\frac{1}{1-(-1)}\int_{-1}^{1}20x+x^3 dx\)\(\displaystyle =\frac{1}{2}[10x^2+(\frac{1}{4})(x)^4] |_-1^1=\frac{1}{2}(10+\frac{1}{4}-10-\frac{1}{4})=0\)

Example Question #9 : Find Average Value

Let \(\displaystyle f(x)=4x+11\). What value of c allows the average value of \(\displaystyle f(x)\) over the interval \(\displaystyle [0,c]\) to be \(\displaystyle 27\)?

Possible Answers:

\(\displaystyle 8\)

\(\displaystyle 6\)

\(\displaystyle 2\)

\(\displaystyle 4\)

Correct answer:

\(\displaystyle 8\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function, average value, and interval to solve for \(\displaystyle c\).

\(\displaystyle 27=\frac{1}{c-0}\int_{c}^{0}4x +11 dx\)

Next, the definite integral can be taken to continue solving for \(\displaystyle c\).

\(\displaystyle 27=\frac{1}{c}[2x^2+11x] |_0^c\)

\(\displaystyle 27=(\frac{1}{c})(2c^2+11c)\)

\(\displaystyle 27=2c+11\)

\(\displaystyle c=8\)

Example Question #10 : Find Average Value

Let \(\displaystyle f(x)=3x2+4x-3\). What value of \(\displaystyle c\) allows the average value of \(\displaystyle f(x)\) over the interval \(\displaystyle [0,c]\) to be \(\displaystyle 12\)?

Possible Answers:

\(\displaystyle -5\)

\(\displaystyle 5\)

\(\displaystyle 3\)

\(\displaystyle -3\)

Correct answer:

\(\displaystyle 3\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation allows the substitution of the function, average value, and interval to solve for \(\displaystyle c\).

\(\displaystyle 12=\frac{1}{c-0}\int_{0}^{c}3x^2+4x-3 dx\)

Next, the definite integral can be taken to continue solving for \(\displaystyle c\).

\(\displaystyle 12=\frac{1}{c}[x^3+2x^2-3x] |_0^c\)

\(\displaystyle 12=(\frac{1}{c})(c^3+2c^2-3c)\)

\(\displaystyle 12=c^2+2c-3\)

\(\displaystyle 0=c^2+2c-15\)

\(\displaystyle 0=(c+5)(c-3)\)

\(\displaystyle c={-5,3}\)

Because the problem states that \(\displaystyle c>0\), the answer \(\displaystyle c=-5\) can be eliminated. Therefore, the correct answer is \(\displaystyle c=3\).

Example Question #1 : Find Average Value

Which of the following theorems is related to finding the Average Value of a Function?

Possible Answers:

Extreme Value Theorem

Mean Value Theorem for Integrals

Fundamental Theorem of Calculus

Intermediate Value Theorem

Correct answer:

Mean Value Theorem for Integrals

Explanation:

The following equation is used for finding the Average Value of a Function:  \(\displaystyle f_{avg}=\frac{1}{b-a} \int_{a}^{b} f(x) dx\). A rearrangement of this equation could be multiplying \(\displaystyle (b-a)\) to both sides. Making this rearrangement, and substituting \(\displaystyle f_{avg}=f(c)\) with \(\displaystyle a< c< b\), results in the following: \(\displaystyle \int_{a}^{b}f(x) dx=f(c)(b-a)\). Assuming \(\displaystyle f(x)\) is continuous, this is the correct equation for the Mean Value Theorem for Integrals.

Example Question #2 : Find Average Value

Find the average value of the function \(\displaystyle f(x)=2x^7+5x^2+4\) over the interval \(\displaystyle [1,3]\). Round to the nearest hundredth.

Possible Answers:

\(\displaystyle 846.50\)

\(\displaystyle 103.45\)

\(\displaystyle 845.67\)

\(\displaystyle 1691.33\)

Correct answer:

\(\displaystyle 845.67\)

Explanation:

When finding the average value of a function, it is useful to keep the following formula in mind: \(\displaystyle f_{avg}=\frac{1}{b-a}\int_{a}^{b}f(x) dx\). This equation is very helpful because it provides a simple way to determine the average value by substituting in values of the bounds and the function itself:

\(\displaystyle f_{avg}=\frac{1}{3-1}\int_{1}^{3}2x^7+5x^2+4 dx=(12)[\frac{1}{4}x^8+\frac{5}{3}x^3+4x] |_1^3\)\(\displaystyle =(\frac{1}{2})(\frac{6561}{4}+45+12-1\frac{}{4}-\frac{5}{3}-4)=845.67\)

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