In this triangle \(a^2 = b^2 + c^2\) and angle \(A\) is a right angle. Pythagoras' theorem only works for right-angled triangles, so you can use it to test whether a triangle has a right angle or not.

If the side of a triangle is extended, the angle formed outside the triangle is the exterior angle. \(g\) is the interior angle. \(h\) is the exterior angle. \(g + h = 180^\circ\) The interior ...