By the way your X is my C. The Pythagorean theorem is a^2+b^2=c^2. A is 12, and b is 16, you would first plug them in. 12^2+16^2=c^2. So then you square them. You would then get 144+256=c^2. So now you add and get 400=c^2. Now find the square root of both sides to get just c. The square root of 400 is 20 and the square root of c^2 is just c. So that means 20=c or in your case x=20.
