Hi

Could someone please explain this substitution problem? I keep getting the wrong answer :s

∫ [(9x) / ((x^4)+1)] dx

Thank-you!

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- Sep 19th 2009, 11:11 AMkinto[SOLVED] substitution indefinite integrals
Hi

Could someone please explain this substitution problem? I keep getting the wrong answer :s

∫ [(9x) / ((x^4)+1)] dx

Thank-you! - Sep 19th 2009, 11:52 AMgalactus
$\displaystyle \int\frac{9x}{x^{4}+1}dx$

Let $\displaystyle u=x^{2}, \;\ \frac{du}{2}=dx$

This gives:

$\displaystyle \frac{9}{2}\int\frac{1}{u^{2}+1}du$

Now, it's easy.