Naming by Angles

Triangles are also sorted by their largest angle. An acute triangle has three acute angles. A right triangle has one right angle. An obtuse triangle has one obtuse angle. A triangle can never have two right angles or two obtuse angles, because its three angles add to 180°. So every triangle gets exactly one of these three names.

A right triangle with its two legs and its hypotenuse

A right triangle has names for its sides too. The two sides that meet at the right angle are the legs. The side opposite the right angle is the hypotenuse. The hypotenuse is always the longest side of a right triangle. A triangle has one name by its sides and one name by its angles, and you can use both together. For example, a triangle can be a right isosceles triangle, or an obtuse scalene triangle.