Since the largest side corresponds to the hypotenuse of a right triangle, we can draw the following picture:
Then, if the triangle is a right one, Pythagorean theorem must be fulfilled. This indicates that the sum of each of the squared legs must be equal to the hypotenuse squared, that is,
[tex]12^2+16^2=20^2[/tex]which gives
[tex]144+256=400[/tex]The left hand side is equal to 400, so we have that
[tex]400=400[/tex]so the sides belong to a righ triangle. So, Is the angle A a right angle? Answer: YES
