I don't get the pythagorean theorem

How does it work ?
How do you find the value of one of the legs of a triangle?
I know that The legs squared (a squared + b squared = C squared, where C is the hypotenuse) but how do you find the value of a leg if you have the value of a hypotenuse and a leg ?

>>14

http://www.4chan.org/rules#global
2. If you are under the age of 18, or it is illegal for you to view the materials contained on this website, discontinue browsing immediately.