Write the expression as the sine, cosine, or tangent of an angle.

sin 9x cos x - cos 9x sin x

Question

Write the expression as the sine, cosine, or tangent of an angle.

sin 9x cos x - cos 9x sin x

anonymous · Answer

here are my choices 

sin 10x

cos 8x

sin 8x

cos 10x

tkhunny · Answer

Have you considered the identity: $\sin(a-b) = \sin(a)\cos(b) - \cos(a)\sin(b))$

anonymous · Answer

no i really dont understand

tkhunny · Answer

I do not believe it.  Why have you been given this problem if you have no way to solve it?  Look at that formula I wrote, especially the right-hand side.  Compare it to your problem statement.  You must see the similarity or you cannot solve this problem.

anonymous · Answer

i really just need the answer im am being timed and my class is about to end please help

tkhunny · Answer

If you will just look at it, you will be done.  Stop telling yourself you can't do it.  As soon as you see the similarity, the solution will present itself.

anonymous · Answer

yea i found the answer no thanks to you

tkhunny · Answer

You mean someone did the work for you.  Oh well, maybe you'll learn from that.