Calculus 2 : Integrals

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #142 : Finding Integrals

If \displaystyle f{}'(x)=2x+1 and \displaystyle f(1)=3, what is the original f(x) function?

Possible Answers:

\displaystyle f(x)=x^2+x+1

\displaystyle f(x)=2x^2+x+1

\displaystyle f(x)=x^2+x-1

\displaystyle f(x)=x^2-x+1

\displaystyle f(x)=x^2+x

Correct answer:

\displaystyle f(x)=x^2+x+1

Explanation:

First, set up the integral expression:

\displaystyle \int 2x+1dx

Now, integrate. Remember to raise the exponent by 1 and then put that result on the denominator:

\displaystyle \frac{2x^2}{2}+x=x^2+x+C

Plug in your initial conditions to find C:

\displaystyle 1^2+1+C=3; C=1

Now plug back in to get your initial f(x) function:

\displaystyle f(x)=x^2+x+1

Example Question #143 : Finding Integrals

Evaluate.

\displaystyle \int_{1}^{2} \frac{1}{2} x \ dx

Possible Answers:

\displaystyle \frac{2}{3}

\displaystyle \frac{9}{8}

Answer not listed.

\displaystyle \frac{5}{7}

\displaystyle \frac{1}{5}

Correct answer:

Answer not listed.

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) = \frac{1}{2} x.

The antiderivative is  \displaystyle F(x) = \frac{1}{4} x^2.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{1}^{2} \frac{1}{2} x \ dx = \left (\frac{1}{4} x^2 \right )_{1}^{2}

\displaystyle = \frac{1}{4} (2)^2 - \left ( \frac{1}{4} (1)^2 \right )

\displaystyle = \frac{3}{4}

Example Question #144 : Finding Integrals

Evaluate.

\displaystyle \int_{12}^{14} e^ {x -7}\ dx

Possible Answers:

\displaystyle 573.8

\displaystyle 1,579.4

Answer not listed.

\displaystyle 232.4

\displaystyle 948.2

Correct answer:

\displaystyle 948.2

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) = e^ {x -7}.

The antiderivative is  \displaystyle F(x) = e^ {x -7}.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{12}^{14} e^ {x -7}\ dx = \left (e^ {x -7} \right )_{12}^{14}

\displaystyle = e^ {14 -7} - \left ( e^ {12 -7} \right )

\displaystyle = 948.2

Example Question #145 : Finding Integrals

Evaluate.

\displaystyle \int_{6}^{7} \frac{x-4}{x-5} \ dx

Possible Answers:

\displaystyle 18.3

\displaystyle 3.5

\displaystyle 16.7

\displaystyle 45.2

Answer not listed.

Correct answer:

Answer not listed.

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) =\frac{x-4}{x-5}.

The antiderivative is  \displaystyle F(x) =\ln(x-5) + x.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{6}^{7} \frac{x-4}{x-5} \ dx = \left (\ln(x-5) + x \right )_{6}^{7}

\displaystyle = \ln(7-5) + 7 - \left ( \ln(6-5) + 6 \right )

\displaystyle = 13.7

Example Question #146 : Finding Integrals

Evaluate.

\displaystyle \int_{0}^{1} \cos(2x-9) \ dx

Possible Answers:

\displaystyle -4.2

\displaystyle 1.54

Answer not listed.

\displaystyle 3.8

\displaystyle 0.02

Correct answer:

\displaystyle 0.02

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) = \cos(2x-9).

The antiderivative is  \displaystyle F(x) = \frac{\sin(2x-9)}{2}.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{0}^{1} \cos(2x-9) \ dx = \left ( \frac{\sin(2x-9)}{2} \right )_{0}^{1}

\displaystyle = \frac{\sin(2(1)-9)}{2} - \left ( \frac{\sin(2(0)-9)}{2} \right )

\displaystyle = 0.02

Example Question #147 : Finding Integrals

Evaluate.

\displaystyle \int_{1}^{2} -\frac{\sin(2x)}{2} \ dx

Possible Answers:

\displaystyle -2.03

\displaystyle 2.04

\displaystyle -0.06

Answer not listed.

\displaystyle 1.38

Correct answer:

\displaystyle -0.06

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) = -\frac{\sin(2x)}{2}.

The antiderivative is  \displaystyle F(x) = \frac{\cos(2x)}{4}.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{1}^{2} -\frac{\sin(2x)}{2} \ dx= \left ( \frac{\cos(2x)}{4} \right )_{1}^{2}

\displaystyle = \frac{\cos(2(2))}{4} - \left ( \frac{\cos(2(1))}{4} \right )

\displaystyle = -0.06

Example Question #148 : Finding Integrals

Evaluate.

\displaystyle \int_{2}^{3}\sec^2 (12x-1)\ dx

Possible Answers:

\displaystyle 0.02

Answer not listed.

\displaystyle 2.74

\displaystyle 0.94

\displaystyle 4.26

Correct answer:

\displaystyle 0.02

Explanation:

\displaystyle \int_{a}^{b} f(x) dx

In this case, \displaystyle f(x) =\sec^2 (12x-1).

The antiderivative is  \displaystyle F(x) = \frac{\tan(12x-1)}{12}.

Using the Fundamental Theorem of Calculus, evaluate the integral using the antiderivative: 

\displaystyle \int_{2}^{3}\sec^2 (12x-1)\ dx = \left ( \frac{\tan(12x-1)}{12} \right )_{2}^{3}

\displaystyle = \frac{\tan(12(3)-1)}{12} - \left ( \frac{\tan(12(2)-1)}{12} \right )

\displaystyle = 0.02

Example Question #149 : Finding Integrals

\displaystyle \int_{0}^{2}x^3+4x^2-x+1dx

Possible Answers:

\displaystyle \frac{43}{3}

\displaystyle \frac{50}{3}

\displaystyle \frac{41}{3}

\displaystyle \frac{38}{3}

\displaystyle \frac{44}{3}

Correct answer:

\displaystyle \frac{44}{3}

Explanation:

First, integrate this expression. Remember to raise the exponent by 1 and then put that result on the denominator:

\displaystyle \frac{x^4}{4}+\frac{4x^3}{3}-\frac{x^2}{2}+x

Now, evaluate at 2 and then 0. Subtract the results:
\displaystyle (\frac{16}{4}+\frac{32}{3}-\frac{4}{2}+2)-0=4+\frac{32}{3}-2+2=\frac{44}{3}

Example Question #150 : Finding Integrals

\displaystyle \int_{1}^{2}x^{\frac{3}{4}}dx

Possible Answers:

\displaystyle 2.3456

\displaystyle 1.2950

\displaystyle 3.5069

\displaystyle 1.3506

\displaystyle 1.8058

Correct answer:

\displaystyle 1.3506

Explanation:

First, integrate this expression. Remember to add one to the exponent and then also put that result on the denominator:

\displaystyle \frac{x^{\frac{7}{4}}}{\frac{7}{4}}

Simplify:

\displaystyle \frac{4}{7}(x^{\frac{7}{4}})

Evaluate at 2 and then 1. Subtract the results:

\displaystyle (\frac{4}{7}(2^{\frac{7}{4}}))-(\frac{4}{7}(1^{\frac{7}{4}}))

Round to four places:

\displaystyle 1.9220-.5714=1.3506

 

Example Question #491 : Integrals

\displaystyle \int_{1}^{4}\frac{5+x^2}{x}dx

Possible Answers:

\displaystyle 9.4315

\displaystyle 12.4315

\displaystyle 14.4372

\displaystyle 14.4315

\displaystyle 14.4328

Correct answer:

\displaystyle 14.4315

Explanation:

First, chop up the fraction into two separate terms:


\displaystyle \int \frac{5}{x}+xdx

Now, integrate:

\displaystyle 5ln\left | x \right |+\frac{x^2}{2}

Evaluate at 4 and then at 1. Subtract the results:

\displaystyle (5ln4+8)-(5ln1+\frac{1}{2})

Round to four places:
\displaystyle 14.9315-.5=14.4315

 

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