Common Core Standard: 6.GA.1 6th Grade Math

Which of these triangles would be isosceles? Related Sites covering Isosceles Triangles

How to prove a Triangle is Isosceles

Isosceles Triangle Theorems VIDEO

Two equal angles and sides so it is an isosceles triangle

Two equal angles and sides so it is an isosceles triangle

Three different angle measures and three unequal sides so it is not an isosceles triangle

The Perimeter formula of an Isosceles Triangles = 2a + b

a =legs

b = base

Area Formula = 1/2 base x height

In order to be classified as an isosceles a triangle it must have two equal legs and two equal angles .

Measure Angle of IsoscelesTriangle ABC equals

Side Length of Isosceles Triangle ABC equals

Theorem: If two sides of a triangle are congruent, then the angles opposite the sides are congruent

Theorem: If two angles of a triangle are congruent, then the sides opposite the angles are congruent

The altitude to the base of an isosceles triangle bisects the vertex angle.

The altitude to the base of an isosceles triangle bisects the base.

Vertex angle of an isosceles triangle is the non congruent angle in an isosceles triangle. The vertex angle is always opposite the base.

The base angles are the angles that are opposite the pair of equal sides of the triangle. (<C and < B)

Given a vertex angle of 110 °, what is the measure of your base angles?

Step 1. The interior measure of a triangle equals 180 therefore 180-110 =70

Step 2. Each base angle is opposite a congruent side and therefore are congruent.

As a result, 70÷2 = 35 ° which equals the measure of each base angle

What is the measure of your vertex given a base angle of 70°?

Step 1 Each base angle is congruent therefore, 70 x2 = 140

Step 2. Interior angle measure triangle = 180 therefore 180 -140 = 40°

VIDEO

The altitude of an isosceles triangles forms two congruent triangles

Vertex angle of an isosceles triangle

Isosceles triangle theorems