# Compound Angle Formula Proof [sin(A+B)]

• July 20th 2008, 02:02 AM
Simplicity
Compound Angle Formula Proof [sin(A+B)]
Hello!

I came across a question to prove:

$\sin (A+B) = \sin A \cos B + \cos A \sin B$

I did it geometrically but the method was fairly long (but it worked). I got told that I could have done it using complex numbers.

How would I do that? Thanks in advance. (Smile)
• July 20th 2008, 03:24 AM
kalagota
$e^{i(A+B)}=e^{iA}e^{iB}$

just solve both sides, by transforming each to trigonometric form..