Calculus 2 : Finding Integrals

Study concepts, example questions & explanations for Calculus 2

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Example Questions

Example Question #131 : Definite Integrals

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

Possible Answers:

\displaystyle 12.4315

\displaystyle 14.4372

\displaystyle 14.4328

\displaystyle 9.4315

\displaystyle 14.4315

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

 

Example Question #132 : Definite Integrals

\displaystyle \int \frac{5x^2-x+10}{5}dx

Possible Answers:

\displaystyle \frac{x^3}{3}-\frac{x^2}{11}+2x+C

\displaystyle \frac{x^3}{4}-\frac{x^2}{10}+2x+C

\displaystyle \frac{x^3}{3}-\frac{x^2}{10}+2x+C

\displaystyle \frac{x^3}{3}-\frac{x^2}{10}+2x

\displaystyle \frac{x^3}{3}-\frac{x^2}{10}-2x

Correct answer:

\displaystyle \frac{x^3}{3}-\frac{x^2}{10}+2x+C

Explanation:

First off, chop up the fraction into three separate terms:

\displaystyle \int x^2-\frac{1}{5}x+2dx

Integrate. Remember to raise the exponent by 1 and then also put that result on the denominator:

\displaystyle \frac{x^3}{3}-\frac{1}{5}(\frac{x^2}{2})+2x

Simplify and add C because it is an indefinite integral:

\displaystyle \frac{x^3}{3}-\frac{x^2}{10}+2x+C

 

Example Question #153 : Finding Integrals

\displaystyle \int_{1}^{5}\frac{7+x}{x}dx

Possible Answers:

\displaystyle 15.3886

\displaystyle 15.8661

\displaystyle 12.2661

\displaystyle 15.2661

\displaystyle 15.2689

Correct answer:

\displaystyle 15.2661

Explanation:

First off, chop up the fraction into two separate terms:

\displaystyle \int \frac{7}{x}+1dx

Now integrate:

\displaystyle 7lnx+x

Evaluate at 5 and then 1. Subtract the results.

\displaystyle (7ln5+5)-(7ln1+1)

Round to four places:

\displaystyle 15.2661

Example Question #152 : Finding Integrals

Integrate \displaystyle f(x)=\frac {x^2}{\sqrt{x}} from \displaystyle [1,4].

Possible Answers:

\displaystyle 12

\displaystyle \frac {62}{5}

None of the Above

\displaystyle \frac {-62}{5}

\displaystyle \frac {60}{7}

Correct answer:

\displaystyle \frac {62}{5}

Explanation:

Step 1: Rewrite the denominator as x to a certain power. A square root means that the exponent will have a value of \displaystyle \frac {1}{2}.

We get \displaystyle x^{\frac {1}{2}}.


Step 2: Divide the numerator and denominator of the function. When we divide terms with exponents, we must make sure that the bases are the same. Both bases are \displaystyle x, so let's continue. When you divide exponents, you are subtracting them. You subtract the bottom exponent FROM the top exponent. 
We get \displaystyle 2-\frac {1}{2}. We will convert the \displaystyle 2 into a fraction with denominator \displaystyle 2. By default, the denominator is \displaystyle 1. We will multiply the numerator and denominator by 2, so the new fraction is \displaystyle \frac {4}{2}.

Step 3: Subtract the converted fraction (exponent of top) and the exponent of the bottom.

\displaystyle \frac {4}{2}-\frac {1}{2}=\frac {4-1}{2}=\frac {3}{2}.

The exponent of the \displaystyle x term is \displaystyle \frac {3}{2}.

Step 4: Integrate...
When we Integrate, we add \displaystyle 1 to the exponent. We then divide the new function with a new exponent by that new exponent.

So, we get: \displaystyle \frac {x^{\frac {3}{2}+1}}{\frac {3}{2}+1}.

Evaluate \displaystyle \frac {3}{2}+1 and then rewrite..
\displaystyle \frac {3}{2}+1=\frac {3}{2}+\frac {2}{2}=\frac {3+2}{2}=\frac {5}{2}

We get: \displaystyle \frac {x^{\frac {5}{2}}}{\frac {5}{2}}

Step 5: Evaluate the upper and the lower limit:

If \displaystyle x=4:

\displaystyle \frac {4^{\frac {5}{2}}}{\frac {5}{2}}=\frac {\sqrt{4^5}}{\frac {5}{2}}=\frac {\sqrt{1024}}{\frac {5}{2}}=\frac {32}{\frac {5}{2}}
Flip the denominator and multiply:

\displaystyle 32 \cdot \frac {2}{5}=\frac {64}{5}

If \displaystyle x=1
\displaystyle \frac{1^\frac{5}{2}}{\frac{5}{2}}=\frac{1}{\frac{5}{2}}=\frac{1}{1}\times\frac{2}{5}=\frac{2}{5}

Step 6:

Subtract lower limit from the upper limit:

\displaystyle \frac{64}{5}-\frac{2}{5}=\frac{62}{5}

Example Question #141 : Definite Integrals

Evaluate \displaystyle \int_{-3}^3 \sqrt{9-x^2} dx.

Possible Answers:

The integral cannot be evaluated.

\displaystyle \pi

\displaystyle 1

\displaystyle \frac{9\pi}{2}

\displaystyle \frac{7\pi}{2}

Correct answer:

\displaystyle \frac{9\pi}{2}

Explanation:

This integral cannot be evaluated using the Fundamental Theorem of Calculus, since an antiderivative does not exist for \displaystyle \sqrt{9-x^2}. Instead, we need to find the area under the curve \displaystyle y=\sqrt{9-x^2} bounded by the \displaystyle x-axis.

 

\displaystyle y=\sqrt{9-x^2} from \displaystyle -3< x< 3, is the graph of the upper half of the circle \displaystyle y^2+x^2=3^2. The area of this upper half is

\displaystyle \frac{\pi r^2}{2} = \frac{\pi(3)^2}{2} = \frac{9\pi}{2}.

Hence \displaystyle \int_{-3}^3 \sqrt{9-x^2}dx=\frac{9\pi}{2}

 

Example Question #151 : Finding Integrals

\displaystyle \int_{0}^{2}\frac{2+x}{x}dx

Possible Answers:

\displaystyle 1.5863

\displaystyle 3.3863

\displaystyle 3.3898

\displaystyle 2.3863

\displaystyle 3.3274

Correct answer:

\displaystyle 3.3863

Explanation:

First, chop up the fraction into two separate fractions:

\displaystyle \int \frac{2}{x}+1dx

Now, integrate:

\displaystyle 2ln\left | x \right |+x

Next, evaluate at 2 and then at 0. Subtract the results:

\displaystyle 2ln(2)+2-(2ln(0)+0)=3.3863.

Example Question #142 : Definite Integrals

\displaystyle \int_{1}^{3}x^2-4xdx

Possible Answers:

\displaystyle \frac{26}{3}

\displaystyle \frac{14}{3}

\displaystyle \frac{22}{3}

\displaystyle \frac{74}{3}

\displaystyle \frac{94}{3}

Correct answer:

\displaystyle \frac{74}{3}

Explanation:

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

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

Simplify to get:

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

Now, evaluate at 3 and then at 1. Subtract the results:
\displaystyle (9+18)-(\frac{1}{3}+2)=27-(2\frac{1}{3})=\frac{74}{3}

Example Question #143 : Definite Integrals

\displaystyle \int_{0}^{3}x^{\frac{4}{5}}dx

Possible Answers:

\displaystyle 4.0297

\displaystyle 4.0172

\displaystyle 4.0283

\displaystyle 3.0137

\displaystyle 4.0137

Correct answer:

\displaystyle 4.0137

Explanation:

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

\displaystyle \frac{x^{\frac{9}{5}}}{\frac{9}{5}}

Simplify to get:

\displaystyle \frac{5}{9}x^{\frac{9}{5}}

Now, evaluate at 3 and then 0. Subtract the results:

\displaystyle (\frac{5}{9}(3)^{\frac{9}{5}})-(\frac{5}{9}(0)^{\frac{9}{5}})=4.0137

Example Question #152 : Finding Integrals

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

Possible Answers:

\displaystyle 11

\displaystyle 16

\displaystyle 9

\displaystyle 12

\displaystyle 13

Correct answer:

\displaystyle 12

Explanation:

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

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

Now, evaluate at 2 and then 1:

\displaystyle (8+8-2)-(1+2-1)=14-2=12.

Example Question #145 : Definite Integrals

\displaystyle \int_{0}^{1}x^{\frac{1}{7}}dx

Possible Answers:

\displaystyle \frac{1}{8}

\displaystyle \frac{7}{8}

\displaystyle \frac{2}{3}

\displaystyle \frac{9}{8}

\displaystyle \frac{1}{4}

Correct answer:

\displaystyle \frac{7}{8}

Explanation:

Recall that when integrating, you must raise the exponent by 1 and also put that result on the denominator:

\displaystyle \frac{x^{\frac{8}{7}}}{\frac{8}{7}}

Simplify to get:
\displaystyle \frac{7}{8}x^{\frac{8}{7}}

Now, evaluate at 1 and then at 0:

\displaystyle (\frac{7}{8}1^{\frac{8}{7}})-(\frac{7}{8}0^{\frac{8}{7}})=\frac{7}{8}

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