Simplify and write the trigonometric expression in terms of sine and cosine:

http://webwork.mathstat.concordia.ca...ac79325181.png

I put this as my answer

http://webwork.mathstat.concordia.ca...5d0e7888d1.png and I was told this Your answer isn't a number

(it looks like a formula that returns a number) I am figuring I have to reduce this?