Originally Posted by

**jezzyjez** I have this integral i need to do in the middle of a engineering question and I have looked in a few directions at it and cant seem to crack it!

The integral is

$\displaystyle \int 4r/\sqrt{2-r^2}$

First I took out factor of 4.

Then multiplyed out the square to get

$\displaystyle 4\int(2r-r^3/2-r^2)$

And tried by parts, which didn't go to well.

So im looking at substitution making

$\displaystyle u = 2r -r^3$

so $\displaystyle du = 2-3r^2 dr$

Where do I go from here ....