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Home / Calculus II / Integration Techniques / Integrals Involving Roots
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Section 7.5 : Integrals Involving Roots

2. Evaluate the integral 1w+21w+2dw.

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Start Solution

The substitution we’ll use here is,

u=1w Show Step 2

Now we need to get set up for the substitution. In other words, we need so solve for w and get dw.

w=1u2dw=2udu Show Step 3

Doing the substitution gives,

1w+21w+2dw=11u2+2u+2(2u)du=2uu22u3du Show Step 4

This integral requires partial fractions to evaluate. Let’s start with the form of the partial fraction decomposition.

2u(u+1)(u3)=Au+1+Bu3

Setting the coefficients equal gives,

2u=A(u3)+B(u+1)

Using the “trick” to get the coefficients gives,

u=3:6=4Bu=1:2=4AA=12B=32

The integral is then,

2u(u+1)(u3)du=12u+1+32u3du=12ln|u+1|+32ln|u3|+c Show Step 5

The last step is to now do all the back substitutions to get the final answer.

\int{{\frac{1}{{w + 2\sqrt {1 - w} + 2}}\,dw}} = \require{bbox} \bbox[2pt,border:1px solid black]{{\frac{1}{2}\ln \left| {\sqrt {1 - w} + 1} \right| + \frac{3}{2}\ln \left| {\sqrt {1 - w} - 3} \right| + c}}