Thanks,

2. ## Re: expansion of cos

Why not just apply the MacLaurin Series formula to the function cos(x)?

3. ## Re: expansion of cos

Originally Posted by Prove It
Why not just apply the MacLaurin Series formula to the function cos(x)?
Probably can't because this is in Pre-University Trigonometry.

@kjchauhan
My only problems with this as a "proof" is your original statement: $cos(n \theta) = \text{...}$. Was this given?

My other problem is your limit statement: $\lim_{\theta \to 0} \frac{sin ( \theta )}{ \theta } = 1$. Was this given as well?

If they are given, it looks great. If they are not given then you have some more work to do.

-Dan