Module 14 Lesson 6 - Isosceles and Equilateral Triangles SHORT VERSION

Isosceles Triangle

A triangle with 2 sides of equal length and 2 angles of equal size.

Equilateral Triangle

A triangle with 3 equal sides and 3 equal angles, each measuring 60°.

What is the defining characteristic of an isosceles triangle?

It has 2 sides that are the same length and 2 angles that are the same size.

Angle sum of a triangle

The angles of a triangle always add up to 180°.

What is the measure of each angle in an equilateral triangle?

Each angle measures 60°.

Key fact about isosceles triangles

If two sides are equal, the angles across from them are equal too.

How many equal sides does an equilateral triangle have?

It has 3 equal sides.

Helpful trick for identifying equilateral triangles

Every equilateral triangle is also an isosceles triangle.

What does the prefix 'equi-' signify in terms of sides?

It means 'equal', indicating all sides are equal in an equilateral triangle.

Isosceles triangle example

Sides: 4, 4, 7; Angles: 50°, 50°, 80°.

Equilateral triangle example

Sides: 6, 6, 6; Angles: 60°, 60°, 60°.