If the sides have different hash marks, they are not congruent. If the hash mark is the same on one or more sides, then those sides are congruent. Mathematicians show congruency by putting a hash mark symbol through the middle of sides of equal length. The length AB is a number, and the segment is the collection of points that make up the segment. While we designate a segment joining points A and B by the notation, we designate the length of a segment joining points A and B by the notation AB without a segment bar over it. Sides of equal length are called congruent sides. Just as triangles can be classified as acute, obtuse, or right based on their angles, they can also be classified by the length of their sides. The sides of the triangle are line segments AB, AC, and CB. The triangle above could be named in a variety of ways:, or. Then keep the letters in order as you go around the polygon. When naming the triangle, you can begin with any vertex. You can call this triangle ABC or since A, B, and C are vertices of the triangle. The labels of the vertices of the triangle, which are generally capital letters, are used to name a triangle.

There is an established convention for naming triangles. The third angle of the right triangle measures 33°. One of the angles has a measure of 90° as it is a right triangle. The sum of the three angles of a triangle is 180 °.

One of the angles in a right triangle measures 57º.