Question

sina^2θcos^2θ= 1/8 (1-cos4θ)

Answer 1

I just googled your question after fixing the typo, and found all kinds of results.

Here is just one of them:
http://www.algebra.com/algebra/homework/Trigonometry-basics/Trigonometry-basics.faq.question.703828.html

let Google be your friend