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## Homework Statement

This doesn't seem too hard but I can't figure it out. I'm trying to write out a power series expansion for a function, and after a bit of math I've got: [tex]f\left(x\right) = 1 - \frac32 + \frac98 - \frac{27}{48} + \frac{81}{384}... = 1 - \frac{3^1}2 + \frac{3^2}{2*4} - \frac{3^3}{2*4*6} + \frac{3^4}{2*4*6*8}...[/tex]

## Homework Equations

N/A

## The Attempt at a Solution

I just don't know how to express 2*4*6*8...etc. mathematically. Help please?