Classifying Triangles

Section 2.2

The segments that form a triangle are called its sides.

The endpoints of the sides of a triangle are called vertices.

The triangle with vertices R, S, and T is called RST (the triangle RST)

You can classify triangles by their sides

1. A scalene triangle has no congruent sides.

2. An isosceles triangle has at least two congruent sides.

3. An equilateral triangle has three congruent sides.

An equilateral triangle is an isosceles triangle, because an equilateral triangle has "at least two congruent sides".

You can classify triangles by their angles.

1. An equiangular triangle has three congruent angles.

2. An acute triangle has three acute angles. (three angles less than 90⁰)

3. A right triangle has one right angle. (measures exactly 90⁰)

4. An obtuse triangle has one obtuse angle. (greater than 90⁰ but less than 180⁰ )

The Angles of a Triangle Property

The sum of the angle measures of a triangle is 180⁰ .

In TRI , m T + m R + m I = 180⁰