The relationship between legs and hypotenuse of a right triangle is
a^2+b^2=c^2
where a,b are the length of the legs, and c is the length of the hypotenuse.
Without knowing the dimensions of the triangle, we assume the hypotenuse is x, and the legs are 15 and 16.
So the proper relationship is:
15^2+16^2=x^2.