# Math Help - integrating by assumed knowledge

1. ## integrating by assumed knowledge

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?

2. 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?

Substitute $u = x^3 \Rightarrow dx = \frac{du}{3x^2}$.
Substitute $u = x^3 \Rightarrow dx = \frac{1}{3x^2}$.
Actually if $\frac{du}{dx} = 3x^2$ then $dx = \frac{du}{3x^2}$.
Actually if $\frac{du}{dx} = 3x^2$ then $dx = \frac{du}{3x^2}$.