Theory:

Pythagorean Theorem: In a right triangle, the square of the hypotenuse is equal to the sum of the squares of the other two sides.
Theory_3.1.png
 
In the above right triangle \(ABC\), the legs are \(AB\) and \(BC\), and the hypotenuse is \(AC\).
 
So it can be written as, \(AC² = AB² + BC²\).
 
Here \(BC = a, AB = b\) and \(AC = c\).
 
Substituting the known values,
 
\(c² = a² + b²\).