- #1

Shinaolord

- 92

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## Homework Statement

Recognize the series $$3-3^3/3!+3^5/5!-3^7/7!$$ is a taylor series evaluated at a particular value of x. Find the sum

## Homework Equations

Sum of Infinite series = ##a/1-x##

## The Attempt at a Solution

So, I can't figure out what i would us as the ratio (the thing you multiply the term by each time.) I got as far as

$$ \sum\limits_{n=0}^\infty (-1)^n \frac{(x^{2n}))}{2n!} $$ is the series for $$cos(x)$$ evaluated at $$ x=0$$, and the value we're looking at is $$a=3$$.

So, I tried the following

## T(x)= \frac{3}{(\frac{(1-3^2)}{n!})}##

but I'm totally stumped on how to find ##n##.

Any hints?

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