Triangle Angle Sums

Learn and apply triangle angle sums.

Lesson 1 of 53 parts Practice Flashcards

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Interior Angle Sum

Objective: Apply interior angle sum in triangle problems.

A triangle’s three interior angles sum to 180°.

Worked examples

Try itTwo angles in a triangle measure 21° and 41°. What is the total measure of all three angles?Show answer

180°. Every triangle’s interior angles total 180°.

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Objective: Apply interior angle sum in triangle problems.

A triangle’s three interior angles sum to 180°.

Worked examples

Try itTwo angles in a triangle measure 21° and 41°. What is the total measure of all three angles?Show answer

180°. Every triangle’s interior angles total 180°.

Objective: Apply finding a missing angle in triangle problems.

Subtract two known interior measures from 180°.

Worked examples

Try itTwo triangle angles measure 21° and 41°. Find the third angle.Show answer

118°. Subtract the two given angles from 180°: 180−(21+41)=118°.

Objective: Apply classifying triangles by angles in triangle problems.

Acute triangles have three acute angles; right triangles have one right angle; obtuse triangles have one obtuse angle.

Worked examples

Try itA triangle has an angle of 91°. How is it classified by angles?Show answer

Obtuse. One angle exceeds 90°, so the triangle is obtuse.

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