Simplifying Factorials: How to Simplify the Expression (2n-1)! / (2n+1)!

[vanceEE]

Homework Statement

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

How do you simplify this factorial?

 

[vanhees71]

Just write out the factorials. Then you'll see immediately how to simplify the expression.

 

[vanceEE]

Just write out the factorials. Then you'll see immediately how to simplify the expression.

I cannot tell from writing them out.
$$\frac{1*3*5*7*9...(2n-1)!}{3*5*7*9*11...(2n+1)!} $$
Please explain.Edit:
Nvm, I understand. Thank you!

$$\frac{(2n-1)!}{(2n+1)!} = \frac{(2n-1)*(2n-2)*(2n-3)*(2n-4)...2*1}{(2n+1)*(2n)*(2n-1)*(2n-2)...2*1} $$
$$ = \frac{1}{(2n)*(2n+1)} $$

or

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