# Ratio Test for Taylor Expansion of Cosine

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• May 7th 2010, 06:49 PM
p75213
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).

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• May 7th 2010, 07:35 PM
Random Variable
$\frac{(2n)!}{(2n+2)!} = \frac{(2n)!}{(2n+2)(2n+1)(2n)!}$
• May 7th 2010, 08:43 PM
p75213
So it is. Many thanks.