Digits, Grade 8, Volume 1, Homework Helper

7-3: Interior Angles of Triangles

Key Concept

The sum of the measures of the interior angles of a triangle is 180°.

Triangle ABC with vertex A on line t and interior angles 1, 2, and 3, respectively. At vertex A, angles 4, 1, and 5 form a straight angle with line t. AB is one side of angle 4 and AC is one side of angle 5.

Part 1

Example Finding Measures of Third Angles in Triangles

Find the missing angle measure in each triangle.

Four triangles.

Solution

For each triangle, write an equation for the sum of the measures of its interior angles. Then solve for the missing angle measure.

Measure of ∠1

table with 3 rows and 1 column , row1 column 1 , m angle 1 plus 43 degrees plus 32 degrees equals 180 degrees , row2 column 1 , m angle 1 plus 75 degrees equals 180 degrees , row3 column 1 , m angle 1 equals 105 degrees , end table

Measure of ∠2

table with 3 rows and 1 column , row1 column 1 , m angle 2 plus 59 degrees plus 21 degrees equals 180 degrees , row2 column 1 , m angle 2 plus 80 degrees equals 180 degrees , row3 column 1 , m angle 2 equals 100 degrees , end table


End ofPage 237

Table of Contents

Digits, Grade 8, Volume 1, Homework Helper Unit A: Number and Operations Unit B: Proportionality Unit C: Expressions, Equations, and Relationships English/Spanish Glossary Formulas Math Symbols Formulas Measures Properties