Angle Relationships

Learn complementary angles, supplementary angles.

Lesson 1 of 32 parts Practice Flashcards

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Complementary Angles

Objective: Explain complementary angles, apply the stated method, and check its conditions.

Two angles are complementary if their measures sum to 90°. They need not be adjacent. If one angle is acute, its complement is found by subtracting its measure from 90°. Angle units must be consistent across the sum. Complementary angles total 90°, not 180°.

Formulas

$α+β=90°$

Worked examples

Try itAn acute angle measures 7°. Find its complement in degrees.Show answer

Step 1: Complementary angles add to 90°. Step 2: Subtract 7 from 90. Step 3: The complement is 83°.

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Complementary Angles

Objective: Explain complementary angles, apply the stated method, and check its conditions.

Formulas

$α+β=90°$

Worked examples

Try itAn acute angle measures 7°. Find its complement in degrees.Show answer

Step 1: Complementary angles add to 90°. Step 2: Subtract 7 from 90. Step 3: The complement is 83°.

Supplementary Angles

Objective: Explain supplementary angles, apply the stated method, and check its conditions.

Two angles are supplementary if their measures sum to 180°. Adjacent angles forming a straight line are a linear pair and therefore supplementary, but supplementary angles do not have to share a vertex or side. Supplementary does not require adjacency.

Formulas

$α+β=180°$

Worked examples

Try itAn angle measures 21°. Find its supplement in degrees.Show answer

Step 1: Supplementary angles add to 180°. Step 2: Compute 180−21. Step 3: The supplement is 159°.

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