AP Calculus AB : Integrals

Study concepts, example questions & explanations for AP Calculus AB

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Example Questions

Example Question #1 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

A particle at the origin has an initial velocity of  \(\displaystyle 32\)\(\displaystyle m/s\). If its acceleration is given by \(\displaystyle a = -24t^2 + 6t - 8\), find the position of the particle after 1 second.

Possible Answers:

\(\displaystyle 27m\)

\(\displaystyle 18m\)

\(\displaystyle 32m\)

\(\displaystyle 29m\)

\(\displaystyle 24m\)

Correct answer:

\(\displaystyle 27m\)

Explanation:

In this problem, letting \(\displaystyle s(t)\) denote the position of the particle and \(\displaystyle v(t)\) denote the velocity, we know that \(\displaystyle s''(t) = v'(t) = a(t)\). Integrating and working backwards we have,

\(\displaystyle v(t) = \int a(t)dt = \int (-24t^2 + 6t - 8)dt = -8t^3 + 3t^2 -8t + C\)

Plugging in our initial condition, \(\displaystyle v(0) = 32\), we see immediately that \(\displaystyle C = 32\).

Repeating the process again for \(\displaystyle s(t)\), we find that 

 \(\displaystyle s(t) = \int v(t)dt = \int (-8t^3 + 3t^2 -8t +32)dt = -2t^4 + t^3 - 4t^2 + 32t + C\)

Plugging in our initial condition, \(\displaystyle s(0) = 0\) (we started at the origin) we see that \(\displaystyle C = 0\). This gives us a final equation

\(\displaystyle s(t) = -2t^4 + t^3 - 4t^2 + 32t\). The problem asks for \(\displaystyle s(1)\) which is simply \(\displaystyle s(t) = -2(1)^4 + (1)^3 - 4(1)^2 + 32(1) = -4 + 1 - 4 + 32 = 27\)

Example Question #2 : Finding Specific Antiderivatives Using Initial Conditions, Including Applications To Motion Along A Line

Find the integral which satisfies the specific conditions of \(\displaystyle (\frac{\pi}{2}, 4)\)

\(\displaystyle \int4sin(t)-12cos(t)+3t^2dt\)

Possible Answers:

\(\displaystyle y=-4tcos(t)-12tsin(t)+t^3\)

\(\displaystyle y=4cos(t)+12sin(t)+t^3\)

\(\displaystyle y=-4cos(t)-12sin(t)+t^3+12.12\)

\(\displaystyle y=-16tan(t)+t^3+12.12\)

Correct answer:

\(\displaystyle y=-4cos(t)-12sin(t)+t^3+12.12\)

Explanation:

Find the integral which satisfies the specific conditions of \(\displaystyle (\frac{\pi}{2}, 4)\)

\(\displaystyle \int4sin(t)-12cos(t)+3t^2dt\)

To do this problem, we need to recall that integrals are also called anti-derivatives. This means that we can calculate integrals by reversing our integration rules.

Furthermore, to find the specific answer using initial conditions, we need to find our "c" at the end.

Thus, we can have the following rules.

\(\displaystyle \int sin(t)dt = -cos(t)+c\)

\(\displaystyle \int cos(t)dt = sin(t)+c\)

\(\displaystyle \int t^ndt=\frac{t^{n+1}}{n+1}+c\)

Using these rules, we can find our answer:

\(\displaystyle \int4sin(t)-12cos(t)+3t^2dt\) 

Will become:

\(\displaystyle -4cos(t)-12sin(t)+\frac{3t^3}{3}+c=-4cos(t)-12sin(t)+t^3+c\)

And so our anti-derivative is:

\(\displaystyle -4cos(t)-12sin(t)+t^3+c\)

Now, let's find c. First set our above expression equal to y

\(\displaystyle y= -4cos(t)-12sin(t)+t^3+c\)

Next, plug in   for y and t. Then solve for c

\(\displaystyle 4= -4cos(\frac{\pi}{2})-12sin(\frac{\pi}{2})+(\frac{\pi}{2})^3+c\)

Looks a bit messy, but we can clean it up to get:

\(\displaystyle 4= 0-12+3.88+c\rightarrow 4=-8.12+c\rightarrow c=12.12\)

Now, to solve, simply replace c with 12.12

\(\displaystyle y=-4cos(t)-12sin(t)+t^3+12.12\)

Example Question #1 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{The function }f(x)\text{ has the following values on the interval }x=[-2,13]:\\&f(-2)=5\\&f(1)=-19\\&f(4)=5\\&f(7)=-6\\&f(10)=-18\\&f(13)=0\\&\\&\text{Approximate the integral of }f(x)\text{ on this interval using right Riemann sums.}\end{align*}\)

Possible Answers:

\(\displaystyle 495\)

\(\displaystyle -495\)

\(\displaystyle -114\)

\(\displaystyle -99\)

Correct answer:

\(\displaystyle -114\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-2)=5\\&f(1)=-19\\&f(4)=5\\&f(7)=-6\\&f(10)=-18\\&f(13)=0\\&\\&\text{Although the total interval has a length of }15\\&\text{Notice the points are equidistant. This distance is our subinterval }3\\&\text{and since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-2}^{13}f(x)\approx3[(-19)+(5)+(-6)+(-18)+(0)]\\&\int_{-2}^{13}f(x)\approx-114\end{align*}\)

Example Question #1 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{Approximate }\int_{-8}^{1}f(x)\\&\text{Using a right Riemann sum, if }f(x)\text{ has the values:}\\&f(-8)=-13\\&f(-5)=-19\\&f(-2)=6\\&f(1)=-9\end{align*}\)

Possible Answers:

\(\displaystyle -315\)

\(\displaystyle -66\)

\(\displaystyle -105\)

\(\displaystyle -35\)

Correct answer:

\(\displaystyle -66\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-8)=-13\\&f(-5)=-19\\&f(-2)=6\\&f(1)=-9\\&\text{Although the total interval has a length of }9\\&\text{Notice the points are equidistant. This distance is our subinterval: }3\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-8}^{1}f(x)\approx3[(-19)+(6)+(-9)]\\&\int_{-8}^{1}f(x)\approx-66\end{align*}\)

Example Question #2 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{Approximate }\int_{-2}^{23}f(x)\\&\text{Using a right Riemann sum, if }f(x)\text{ has the values:}\\&f(-2)=-2\\&f(3)=-15\\&f(8)=14\\&f(13)=15\\&f(18)=-9\\&f(23)=-12\end{align*}\)

Possible Answers:

\(\displaystyle -35\)

\(\displaystyle -9\)

\(\displaystyle -225\)

\(\displaystyle -45\)

Correct answer:

\(\displaystyle -35\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-2)=-2\\&f(3)=-15\\&f(8)=14\\&f(13)=15\\&f(18)=-9\\&f(23)=-12\\&\text{Although the total interval has a length of }25\\&\text{Notice the points are equidistant, with }5\text{ intervals between. Each equidistant interval has length: }5\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-2}^{23}f(x)\approx5[(-15)+(14)+(15)+(-9)+(-12)]\\&\int_{-2}^{23}f(x)\approx-35\end{align*}\)

Example Question #4 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{Approximate }\int_{-7}^{13}f(x)\\&\text{Using a right Riemann sum, if }f(x)\text{ has the values:}\\&f(-7)=18\\&f(-2)=-17\\&f(3)=-16\\&f(8)=-15\\&f(13)=-14\end{align*}\)

Possible Answers:

\(\displaystyle -310\)

\(\displaystyle -220\)

\(\displaystyle -880\)

\(\displaystyle -44\)

Correct answer:

\(\displaystyle -310\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-7)=18\\&f(-2)=-17\\&f(3)=-16\\&f(8)=-15\\&f(13)=-14\\&\text{Although the total interval has a length of }20\\&\text{, notice the points are equidistant, with }4\text{ intervals between.}\\&\text{Each equidistant interval has length: }5\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-7}^{13}f(x)\approx5[(-17)+(-16)+(-15)+(-14)]\\&\int_{-7}^{13}f(x)\approx-310\end{align*}\)

Example Question #1 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&f(4)=9\\&f(6)=10\\&f(8)=-18\\&f(10)=15\\&f(12)=18\\&\text{Approximate, using a right Riemann sum, }\int_{4}^{12}f(x)\end{align*}\)

Possible Answers:

\(\displaystyle 272\)

\(\displaystyle 34\)

\(\displaystyle 68\)

\(\displaystyle 50\)

Correct answer:

\(\displaystyle 50\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(4)=9\\&f(6)=10\\&f(8)=-18\\&f(10)=15\\&f(12)=18\\&\text{Although the total interval has a length of }8\\&\text{, notice the points are equidistant, with }4\text{ intervals between.}\\&\text{Each equidistant interval has length: }2\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{4}^{12}f(x)\approx2[(10)+(-18)+(15)+(18)]\\&\int_{4}^{12}f(x)\approx50\end{align*}\)

Example Question #1 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{The function }f(x)\text{ has the following values on the interval }x=[-2,38]:\\&f(-2)=-13\\&f(6)=-4\\&f(14)=-15\\&f(22)=-19\\&f(30)=18\\&f(38)=-8\\&\text{Approximate the integral of }f(x)\text{ on this interval using right Riemann sums.}\end{align*}\)

Possible Answers:

\(\displaystyle -1640\)

\(\displaystyle -328\)

\(\displaystyle -41\)

\(\displaystyle -224\)

Correct answer:

\(\displaystyle -224\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-2)=-13\\&f(6)=-4\\&f(14)=-15\\&f(22)=-19\\&f(30)=18\\&f(38)=-8\\&\text{Although the total interval has a length of }40\\&\text{, notice the points are equidistant, with }5\text{ intervals between.}\\&\text{Each equidistant interval has length: }8\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-2}^{38}f(x)\approx8[(-4)+(-15)+(-19)+(18)+(-8)]\\&\int_{-2}^{38}f(x)\approx-224\end{align*}\)

Example Question #6 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{Approximate }\int_{0}^{15}f(x)\\&\text{Using a right Riemann sum, if }f(x)\text{ has the values:}\\&f(0)=-19\\&f(5)=14\\&f(10)=2\\&f(15)=15\end{align*}\)

Possible Answers:

\(\displaystyle 60\)

\(\displaystyle 12\)

\(\displaystyle 180\)

\(\displaystyle 155\)

Correct answer:

\(\displaystyle 155\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(0)=-19\\&f(5)=14\\&f(10)=2\\&f(15)=15\\&\text{Although the total interval has a length of }15\\&\text{, notice the points are equidistant, with }3\text{ intervals between.}\\&\text{Each equidistant interval has length: }5\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{0}^{15}f(x)\approx5[(14)+(2)+(15)]\\&\int_{0}^{15}f(x)\approx155\end{align*}\)

Example Question #2 : Riemann Sums (Left, Right, And Midpoint Evaluation Points)

\(\displaystyle \begin{align*}&\text{Approximate }\int_{-8}^{0}f(x)\\&\text{Using a right Riemann sum, if }f(x)\text{ has the values:}\\&f(-8)=7\\&f(-6)=-7\\&f(-4)=16\\&f(-2)=-16\\&f(0)=20\end{align*}\)

Possible Answers:

\(\displaystyle 20\)

\(\displaystyle 160\)

\(\displaystyle 26\)

\(\displaystyle 40\)

Correct answer:

\(\displaystyle 26\)

Explanation:

\(\displaystyle \begin{align*}&\text{A Riemann sum integral approximation over an interval [a, b]}\\&\text{with n subintervals follows the form:}\\&\int_a^b f(x)dx \approx \frac{b-a}{n}(f(x_1)+f(x_2)+...+f(x_n))\\&\text{It is essentially a sum of n rectangles, each with a base of}\\&\text{length :}\frac{b-a}{n}\text{ and variable heights :}f(x_i)\text{, which depend on the function value at }x_i\\&\text{In our case, we have function values over an interval:}\\&f(-8)=7\\&f(-6)=-7\\&f(-4)=16\\&f(-2)=-16\\&f(0)=20\\&\text{Although the total interval has a length of }8\\&\text{, notice the points are equidistant, with }4\text{ intervals between.}\\&\text{Each equidistant interval has length: }2\\&\text{Since we are using the right point of each interval, we disregard the first function value:}\\&\int_{-8}^{0}f(x)\approx2[(-7)+(16)+(-16)+(20)]\\&\int_{-8}^{0}f(x)\approx26\end{align*}\)

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