This is a right triangle: A |\ | \ | \ | \ | \ | \ |90° \ CŻŻŻŻŻŻŻB because one of its angles, C, is 90°. It has three sides. The shorter two sides are AC and BC. They are called the two "legs" The longest side is AB, and it is called the "hypotenuse" The longest side of any right triangle is called the hypotenuse. It is also directly across the triangle from the 90° angle. No other kind of triangle has a hypotenuse except a right triangle. Edwin