# Trigonometry question

1. Aug 29, 2007

### _Andreas

My teacher told me that

C sin(k x) + D cos(k x) = F sin(k x+gamma)

if neither C nor D is 0 (gamma is a phase angle). How do you derive the expression on the right of the equal sign from that on the left?

Last edited: Aug 29, 2007
2. Aug 29, 2007

### neutrino

While normally one would say C and D assume certain values, I'll let you find what those values are. Expand the expression on the right and equate the terms on both sides.

3. Aug 29, 2007

### _Andreas

Actually, I just found out that my course book provides the answer to my question. Sorry for bothering! But thanks anyway.

So, note to self: always look in your books before posting questions here.

4. Aug 29, 2007

### genneth

The relevant trig identity is $$\sin (A+B) = \sin A \cos B + \sin B \cos A$$.