The Pythagorean theorem is a simple theorem that states that - for a right angled triangle the square of the length of the hypotenuse is equal to the sum of the squares of the length of the remaining two sides. In this video, a right angled triangle with three sides, namely a, b and c is shown. One side "a" is of unknown length. The length of the other two sides are given. This problem is then solved using the above mentioned theorem. As expected, a bit of basic algebric manipulation (linear equation solution) is required to obtain the length of a.