Let's say there is a right triangle with sides 6 and 7.
We compute the 3rd side (the hypotenuse) by
hypotenuse² = 6² + 7²
hypotenuse² = 36 +49
hypotenuse² = 85
85 is NOT a perfect square so on a calculator, use the square root function to find the square root of 85 which equals
9.2195444573