# Help on expanding this equation

1. Dec 5, 2005

### ultrabionic_ang

hello.. i've been having some trouble with expanding this:

(B^2+C^2)^(1/2) X sin (omega*t +(taninverse B/C)

(read as: square root of (b squared plus c squared) times sin times the quantity omega times t plus taninverse of B divided by C)

apparently, the answer is supposed to be B cos omega*t + C sin omega*t .. but i've gotten like B arctan omega^2(t) + C cos omega*t... i just wanted to know like the way to get the answer.. i think i'm using trig identities incorrectly..

2. Dec 5, 2005

### Tide

What you need is $\sin (x + y) = \sin x \cos y + \cos x \sin y$ and use the fact that $\sin \tan^{-1} x = x/ \sqrt {1 + x^2}$ and similarly for the cosine.

3. Dec 5, 2005

### ultrabionic_ang

thanks! that helped a lot! thank you!