# Try and intergrate this

1. May 23, 2009

### thomas49th

$$\int \frac{x}{\sqrt(1-4x^{2})}dx$$
If it was just a constant on top I could turn it into an arcsin, but there is a stupid x there, so not to sure. I though about intergrating by parts, but their must be an easier method than that?

Thanks

2. May 23, 2009

### quasar987

Well, you could make the x above "disappear" by doing a change of variable u=4x².

3. May 23, 2009

### Dick

Try the substitution u=1-4x^2.

4. May 23, 2009

### thomas49th

cheers thanks got it!

btw, how do you spot a substitution? There is a rule(s) for it. When somthingis the product or differential of somthing else?

Thanks :)

5. May 23, 2009

### Dick

When you see a multiple of the derivative of something else in the numerator, it's a dead giveaway for a substitution.