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## Homework Statement

What is [tex]\sum_{n=0}^{\infty}{\frac{1}{(2n)!}}[/tex]?

## Homework Equations

[tex]e^x[/tex] = [tex]\sum_{n=0}^{\infty}{\frac{x^n}{n!}}[/tex]

## The Attempt at a Solution

I understand that the given series looks like the series for e^1 but I know that isn't the correct answer. The answer (without solution) was supplied as (1/2)(e+e^-1). I can't seem to figure out the extra e^-1 part. Help?