Pythagorean theorem states that the sum of the squares on the legs of a right triangle is equal to the square on the hypotenuse (the side opposite the right angle)—or,
algebraic notation, a2 + b2 = c2.
Consider ∆ PQR is right-angled at Q; PR is the hypotenuse and PQ, QR are the remaining two sides
then, (PR)2 = PQ2 + QR2
(h)2 = p2 + b2
h → hypotenuse
p → perpendicular
b → base