Pythagoras' theorem only works for right-angled triangles, so you can use it to test whether a triangle has a right angle or not.

Does the Pythagorean Theorem formula work on all triangles?

This theorem holds true for this right triangle—the sum of the squares of the lengths of both legs is the same as the square of the length of the hypotenuse. And, in fact, it holds true for all right triangles. ... Note that the Pythagorean Theorem only works with right triangles.

What triangles use the Pythagorean Theorem?

One of the best known mathematical formulas is Pythagorean Theorem, which provides us with the relationship between the sides in a right triangle. A right triangle consists of two legs and a hypotenuse.