From the figure, we can conclude that the little triangle is an isosceles triangle, the greatest angle is 90 because ∠A = 90 and they are supplementary, therefore, using the triangle sum theorem:
A right triangle is a triangle in which one of the angles is a 90∘ angle. The "square" at the vertex of the angle indicates that it is 90 degrees. A triangle can be determined to be a right triangle if the side lengths are known.
