Integration by substitution

rachaelmw

New member
Joined
Jan 16, 2008
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5
First, I apologize for the lack of LaTeX. I do not have the compiler installed on this machine.

The problem I am stuck on asks me to integrate x^3 * sqrt(1-x^2), with u=1-x^2.

To begin, I set u=1-x^2, du = -2x. I also restructured the original problem as follows: x^2 * sqrt(1-x^2) * x

With substitution, this gave me: -1/2 [Integral] (1-u)*sqrt(u) du

However, it all goes downhill from there, and I'm unable to reach what I know to be the correct answer, as provided to me by the professor: -1/15(1 - x^2) ^ 3/2 * (2 + 3x^2)

Any help on where I'm going wrong is greatly appreciated.
 
(-1/2) int (1 - u)*sqrt(u) du = (-1/2) int u[sup:17sqvsw6]1/2[/sup:17sqvsw6] - u[sup:17sqvsw6]3/2[/sup:17sqvsw6] du

can you take it from here?
 
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