Geometry
posted by Nessie .
A^2 , b^2 , c^2 represent

whatever you want them to represent. On right triangles, abc often (but not always) represents a and b are legs, and c is the hypotenuse. But that is not a LAW. I could draw a right triangle labeling the legs gamma, lemma, and the hypotenuse Iota.
If you are using a right triangle with a,b,c, then c^2=a^2+b^2 
What Is a pythgorean Theorem ?