integrating by assumed knowledge

**tsal15** · December 15th 2008, 02:53 PM

ok i've this question:

$\int \frac{3x^2}{\sqrt{1-x^6}}$

I know that the answer is $sin^-1(x^3) + c$

I see the relationship between $sin^-1(x)$ and $sin^-1(x^3)$ and their integrals and this question...But what would be the best method to use to integrate and if it is substitution, what will u equal?

Thanks in advance!!

**mr fantastic** · December 15th 2008, 03:23 PM

Originally Posted by tsal15

ok i've this question:

$\int \frac{3x^2}{\sqrt{1-x^6}}$

I know that the answer is $sin^-1(x^3) + c$

I see the relationship between $sin^-1(x)$ and $sin^-1(x^3)$ and their integrals and this question...But what would be the best method to use to integrate and if it is substitution, what will u equal?

Thanks in advance!!

Substitute $u = x^3 \Rightarrow dx = \frac{du}{3x^2}$ .