Interior angles in a triangle add up to 180˚. Triangles close triangleA polygon with three straight sides. have three sides, therefore they have three angles. Interior angles in a triangle sum to ...

A triangle is a three-sided shape, where the sides are straight and meet at three vertices. The prefix "tri" means three. There are several types of triangles. Do you know what they are?

The triangle angle sum theorem makes working with triangles easy. What happens when you can’t rely on it?