Pythagorean theorem is a relation among the three sides of a right triangle in Euclidean geometry. Ancient Greek mathematician Pythagoras proposed and named the Pythagorean theorem.

Pythagoras proved that the combined area of the two small squares is equal to the area of the big one.
                  Pythagoras Theorem
The Pythagorean theorem states that "the sum of the squares of the lengths of the two other sides of any right triangle will equal the square of the length of the hypotenuse".
                                             Pythagorean Theorem
                      In algebraic terms,Pythagoras theorem is written as
                                        $a^{2} + b^{2} = c^{2}$
      where c is the length of the hypotenuse and a,b are the other sides of the triangle.   
The general formula of Pythagorean theorem is:
           $a^{2} + b^{2} = c^{2}$
 where c is the length of the hypotenuse and a,b are the other sides of the triangle.

To find the hypotenuse c,
         $c = \sqrt{a^{2} + b^{2}}$

To find other sides say a or b,
         $a = \sqrt{c^{2} - b^{2}}$
             or
         $b = \sqrt{c^{2} - a^{2}}$