GM-U2.3 Lesson: Triangle Angle Sum & Parallel Lines

Unit 2 Lesson 3:
Triangle Angle Sum & Parallel Lines

​Goal:

Students are going to use triangle angle sum and angle relationships created by transversals through parallel lines to solve problems.

Concept:

Triangle Angle Sum

The sum of the interior angles of any triangle is 180 degrees.

Procedures: Missing Angles

1) To solve for missing angles of a triangle, write an equation adding the given interior angles and set that sum equal to 180 degrees, then solve.
2) To solve for angles that are exterior, use angle relationships to determine angle types and solve using the properties of angles created by a transversal through parallel lines.

Given: Angle C = 45
Given: Angle A = 85

Solve for the missing angle.

​

​Example 1:

Solve for x.

Give the measures of all angles.

​

ExaMple 2:

What does the measure of x need to be for the horizontal lines to be parallel?

​

example 3: