Evaluating integrals with radicals and fractions

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August 10th 2010, 08:37 PM
bobsanchez

Evaluating integrals with radicals and fractions

Two integration problems are giving me a lot of trouble.

(2x + 2)/(x^2 + 2x)^(1/2)

and

dx/(x^1/2)(1 - x^1/2)^4

I can't get the substitution technique to work out on these two for some reason.
August 10th 2010, 08:42 PM
Prove It

$\int{\frac{2x+2}{(x^2 + 2x)^{\frac{1}{2}}}\,dx} = \int{(2x+2)(x^2+2x)^{-\frac{1}{2}}\,dx}$ .

Let $u = x^2+2x$ so that $du = (2x+2)dx$ and the integral becomes

$\int{u^{-\frac{1}{2}}\,du}$

$= \frac{u^{\frac{1}{2}}}{\frac{1}{2}}+C$

$= 2u^{\frac{1}{2}}+C$

$= 2(x^2+2x)^{\frac{1}{2}}+C$ .
August 10th 2010, 08:49 PM
Prove It

$\int{\frac{dx}{x^{\frac{1}{2}}(1-x^{\frac{1}{2}})^4}} = \int{x^{-\frac{1}{2}}(1-x^{\frac{1}{2}})^{-4}\,dx}$

$= -2\int{-\frac{1}{2}x^{-\frac{1}{2}}(1-x^{\frac{1}{2}})^{-4}\,dx}$ .

Let $u=1-x^{\frac{1}{2}}$ so that $du = -\frac{1}{2}x^{-\frac{1}{2}}\,dx$ and the integral becomes

$-2\int{u^{-4}\,du}$

$= -2\left(\frac{u^{-3}}{-3}\right) + C$

$= \frac{2}{3u^3} + C$

$= \frac{2}{3(1-x^{\frac{1}{2}})^3} + C$ .

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