# Math Help - Ratio Test for Taylor Expansion of Cosine

1. ## Ratio Test for Taylor Expansion of Cosine

Can somebody tell me how the denominator contains (2n+2)(2n+1) in the answer. I am thinking (2n)!/(2n+2)! expands into (2n)!/(2n)!(2n+2). This simplifies into 1/(2n+2).

2. $\frac{(2n)!}{(2n+2)!} = \frac{(2n)!}{(2n+2)(2n+1)(2n)!}$

3. So it is. Many thanks.