Thread: derive cos(alpha+beta) sin(alpha+beta)?

Can someone please help me derive the cos(alpha+beta) sin(alpha+beta)? Preferably in simple language X(

I have to be able to do this on a test tomorrow, please help me

here's a link that may help ...

Math Forum - Ask Dr. Math

Thanks for the link but we're supposed to derive it using matrices.

PlanetMath: addition and subtraction formulas for sine and cosine

on one of the very back pages of googles. this is the same thing right?

i'm goign to ask a really stupid question sorry but...what is this used for?