Let’s start our study of triangles with discussing the three main types of angles. These types are acute angles, right angles, and obtuse angles.
An acute angle is an angle with a measure less than 90º.
A right angle is an angle with a measure of 90º.
An obtuse angle is an angle with a measure greater than 90º.
Recall from geometry that you need three known measures to describe a triangle—the lengths of two sides and the measure of an angle, the lengths of three sides, or three other measures. For a right triangle, you need only two additional measures, because you already know that one of the angles’ measures is ...