Question 101884
The hypotenuse is always the longest side of a right triangle. So knowing this we can plug the length of these sides into the pythagorean formula and prove if it is a right triangle or not. 
The pythagorean formula is:
{{{a^2+b^2=c^2}}}
c is the hypotenuse 
a is one side of the triangle
b is the remaining side of the triangle
Lets see what we get:
{{{a^2+b^2=c^2}}}
{{{16^2+12^2=20^2}}}
{{{256+144=400}}}
{{{400=400}}}
The pythagorean formula only works with right triangles. So we can be sure that the given triangle is a right triangle.