Question

sin40 * cos20 + cos40 * sin20
help... where do I start!?

Answer 1

Hey there! I see that you are new to openstudy.
This is a great website on getting help with questions
of any subject. It is a fun way of learning!
I wish you good luck on openstudy and dont forget to
read the http://openstudy.com/code-of-conduct
so you know the rules and regulations :)
Hope you have fun!

Answer 2

yes, wish i would have found this site earlier this semester! thanks!

Answer 3

Recall the angle sum-difference identity for sine:
\[\sin(\alpha+\beta)=\sin\alpha\cos\beta+\sin\beta\cos\alpha\]
\[\sin40\cos20+\cos40\sin20=\sin(40+20)=\sin60\]
(angles in degrees)