I am going to show you what C2= A2+B2 is:
C2 is the hyptenuse of a right triangle also known as the longer part of it.
A2 is one of the legs in a right triangle which is the height of it.
B2 is the other leg of the right trangle known as the base which tells how long it is.
How you find the hypotenuse is take the A2 + B2 and it gives you a higher number, but you have to square root the number to get a answer.
C2=15cm2 + 39cm2
C2=225cm + 1521cm