Triangle Angle Sum Theorem and Types of Triangles

Triangle Angle Sum Theorem

G.2 Day 2

Learning objective:

●Today I am using CHAMPS expectations so that I can explore angle measurements of triangles.

●I’ll know I got it when I can calculate the missing angle when given the other two angles.

Word Cloud

What do you already know about triangles?

Triangle angle sum theorem

●The sum of the 3 interior angles of a triangle add up to 180°.

●If ∠a, ∠b, & ∠c are the 3 angles of ΔABC, then…

●∠a + ∠b + ∠c = 180°

Open Ended

Examine each set of triangles. What do you notice? What is the same?

I Do

Two angles in a triangle measure 102° and 54°. What is the
measure of the third angle?


Get Ready - Your turn next!

Fill in the Blank

Two angles in a triangle measure 48^o and 62^o . What is the measure of the third angle?

Types of triangles

Equilateral Triangle

• Three equal sides

• Three equal angles,
  always 60°

Isosceles Triangle

• Two equal sides

• Two equal angles

Scalene Triangle

• No equal sides

• No equal angles

Multiple Choice

What type of triangle is this?

• Isosceles

• Equilateral

• Scalene

Multiple Choice

What type of triangle is this?

• Isosceles

• Equilateral

• Scalene

Multiple Choice

What type of triangle is this?

• Isosceles

• Equilateral

• Scalene

Multiple Choice

What type of triangle is this?

• Isosceles

• Equilateral

• Scalene

Fill in the Blank

An isosceles triangle has _____ congruent sides.

Fill in the Blank

An ________ triangle has three congruent sides.

Fill in the Blank

A __________ triangle has no congruent sides.

Types of angles

Acute Triangle

All angles are less
than 90°

Right Triangle

Has a right angle (90°)

Obtuse Triangle

Has an angle more than
90°

Multiple Choice

What type of triangle is this?

• acute triangle

• right triangle

• obtuse triangle

• equilateral triangle

Multiple Choice

What type of triangle is this?

• acute triangle

• right triangle

• obtuse triangle

• equilateral triangle

Multiple Choice

What type of triangle is this?

• acute triangle

• right triangle

• obtuse triangle

• equilateral triangle

Multiple Choice

What type of triangle is this?

• acute triangle

• right triangle

• obtuse triangle

• equilateral triangle