Triangles | Elementary

Triangles - Cycle 3

| Mathematics

What is a triangle?

Definition

A triangle is a three-sided polygon.

Examples:

There are three angles inside every triangle. The sum of a triangle's interior angles is always 180 degrees (°).

Examples

There are different kinds of triangles. Triangles are classified according to the characteristics of their sides and their angles.

Examples

Characteristics	Examples
An equilateral triangle has three congruent sides (of equal measurement).
It also has three congruent 60-degree (°) angles.

Characteristics	Examples
A scalene triangle has three sides with different measurements.
It also has three angles with different measurements.

Characteristics	Examples
An isosceles triangle has two congruent sides (of equal measurement).
It also has two congruent angles.

Characteristic	Examples
A right triangle always contains a right angle (90°).

Be careful!

A right triangle can also be isosceles or scalene.

Isosceles right triangle
It has the main characteristic of a right triangle (a right angle).
It also has the characteristics of an isosceles triangle (two congruent sides and two congruent angles).

Scalene right triangle
It has the main characteristic of a right triangle (a right angle).
It also has the characteristics of a scalene triangle (three sides and three angles of different measurements).

Moments in the video: