Hey guys,(adsbygoogle = window.adsbygoogle || []).push({});

By what rules is the integral of

[tex]\frac{cos(t)}{1+9sin^2(t)}=\frac{1}{3}tan^{-1}(sin(3t))[/tex]

I know this is right, but I have no idea why and can't find any trig identities to help. Thanks.

**Physics Forums | Science Articles, Homework Help, Discussion**

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Tricky Integral

**Physics Forums | Science Articles, Homework Help, Discussion**