EMAT 6690

Day 1  Classification of Triangles

A triangle is a three sided polygon.  A polygon is a closed figure in a plane that is made up of segments called sides that intersect only at their endpoints, called vertices

Parts of a Triangle

One way to classify triangles is by their angles.

All triangles have at least two acute angles, but the third can be acute, right, or obtuse.  A triangle can be classified by using the third angle.

Acute triangle- all the angles of the triangle are acute. Click here for intermath description for acute triangle.

Obtuse triangle- one angle of the triangle is obtuse.

Right triangle- one angle of the triangle is right.

Equiangular triangle- a triangle in which all the angles of the triangle are equal. Click here for intermath info on equilateral triangle.

Triangles can also be classified by according to the number of congruent sides.

Scalene triangle- a triangle in which no two sides are congruent.

Isosceles triangle- a triangle in which at least two sides are congruent.

Equilateral triangle- a triangle in which all the sides are congruent.

Some parts of a  right triangle and isosceles triangle have special names.