Potential Energy of a Pendulum Explained

[fridsatu]

I am sure this is simple to most people...but i don't understand how to show potential energy of a pendulum to be mgcostheta/2l. is there anybody that could break that down for me??

 

[Chi Meson]

First of all, it's not.

PE of a pendulum is mg [L-Lcos(theta/2)].

What's the usual formula for PE? What of the above formula is equal to the "h"?