6^2 + 8^2 = 9^2
36 + 64 = 81
100 = 81.
THIS IS NOT A RIGHT TRIANGLE.
It is acute
A + B = C is something you can use for right triangles. A and B are the smaller angles, and C is the biggest angle. If A + B is bigger than C, then it is an acute triangle. If A + B is less than C, it is obtuse.