Pythagoras’ Theorem or Pythagorean Theorem is named after a Greek philosopher, Pythagoras, who was born around 507 BC in Samos island of old Greece.

According to the diagram:
∠ABC = 90° (AB is perpendicular to BC) & AC is Hypotenuse then:

(AC)² = (AB)² + (BC)²

OR

c² = a² + b²

OR

(Hypotenuse)² = (Perpendicular)² + (Base)²