# Integration with a square root at the bottom

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• Nov 10th 2008, 12:04 PM
!!!
Integration with a square root at the bottom
So I was reviewing my examples, and one of them looked like this:
http://img217.imageshack.us/img217/4295/mathzx1.jpg
and that u = 4x + 1, therefore du = 4dx. But how did the first step above turned into the next step? I can't seem to see how the next part came to be.
• Nov 10th 2008, 12:31 PM
Krizalid
Actually, the substitution given is $u^2=4x+1.$