# Math Help - Arc Length

1. ## Arc Length

I don't understand how to get from this:
$S = 2\pi \int \frac{x^3}{3} \sqrt{1+x^4} dx$ [0,3]
to this:
$
= \frac{\pi}{6} \int (1+x^4)^{1/2}(4x^3) dx$
[0,3]

The only thing I understand really is rewriting the square root.

2. They are the same thing can't you see. It's just reaarangements of coefficients.. And 2/3 = 4/6.

-O