1. May 23, 2009 #1

   thomas49th

   

   [tex]\int \frac{x}{\sqrt(1-4x^{2})}dx[/tex]
   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

    

   thomas49th, May 23, 2009
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3. May 23, 2009 #2

   quasar987

   

   Science Advisor

   Homework Helper

   Gold Member

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

    

   quasar987, May 23, 2009
4. May 23, 2009 #3

   Dick

   

   Science Advisor

   Homework Helper

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

    

   Dick, May 23, 2009
5. May 23, 2009 #4

   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 :)

    

   thomas49th, May 23, 2009
6. May 23, 2009 #5

   Dick

   

   Science Advisor

   Homework Helper

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

    

   Dick, May 23, 2009

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