A triangle has sides with lengths of 9 millimeters, 12 millimeters, and 17 millimeters is it a right triangle?

To find out if it can be a right triangle you use the pythagorean theorem

pythagorean theorem:
a^2 + b^2 = c^2
(c is always the hypotenuse a.k.a. the largest number)

9^2 + 12^2 = 17^2
81 + 144 = 289
225 = 289

because they aren’t equal it couldn’t be a right triangle