Pythagorean theorem

To calculate the longest side (the hypotenuse) of a right triangle in Excel, you can use a formula based on the Pythagorean theorem, adapted to use Excel's math operators and functions. In the example shown, the formula in D5, copied down, is: =SQRT(B5^2+C5^2) which returns the length of the hypotenuse, given lengths of side a and aside b, given in columns B and C respectively.