Question 660337
In other words, find where a^2 + b^2 does NOT equal c^2, which is only true for a right triangle.

A.  Does 5^2+12^2=13^2
25 + 144 = 169 and 13^2=169
Yes, right triangle
B.  Does 8^2+15^2=17^2
64 + 225 = 289 and 17^2=28
Yes, right triangle
C.  Does 9^2+40^2=41^2
81 + 1600 = 1681 and 41^2=1681
Yes, right triangle
D.  Does 20^2+21^2=28^2
400 + 441 = 841 and 28^2=784
No, not a right triangle