Question 963823
The right triangle has two sides, usually one shorter than the other, and the hypotenuse. The hypotenuse is the longest side. Let's call one side a and the other b, and the hypotenuse h
Pythagoras:
{{{h= sqrt(a^2+b^2)}}}
{{{h= sqrt(12^2+9^2)}}}
{{{h= sqrt(144+91)}}}
{{{h= sqrt(235)}}}
{{{h= 15.33}}} is the length of the hypotenuse, which you problem calls "the longest side".