complementary angles

Meaning

1. 1nounplural

   Two angles whose sizes add up to exactly 90 degrees, so that together they make a right angle.

   Grammar: Always about a pair: two angles are complementary angles; one is the complement of the other.

   Patterns

   • angles that are complementary to each other

   A 30-degree angle and a 60-degree angle are complementary angles.

   In a right triangle, the two sharp corners are complementary angles.

   If one of two complementary angles measures 25 degrees, the other must measure 65 degrees.

Word forms

Common combinations

pair of complementary angles

Find a pair of complementary angles in the diagram.

two complementary angles

Two complementary angles share a right angle between them.

measure of complementary angles

The measure of complementary angles always totals 90 degrees.

adjacent complementary angles

Adjacent complementary angles form a right angle.

find the complement

To find the complement, subtract the angle from 90.

Synonyms and how they differ

angles summing to 90 degrees

This phrase explains the idea in plain words, while complementary angles is the exact name.

supplementary angles

Supplementary angles are not a synonym but a related pair that adds up to 180 degrees instead of 90.

Word family

complement noun

the angle that, added to another, makes 90 degrees

complementary adjective

adding up to 90 degrees, or going well together

supplementary angles noun

two angles totaling 180 degrees

right angle noun

an angle of exactly 90 degrees

Commonly confused: complementary angles or complementary vs. complimentary?

Practice

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Write a sentence using “complementary angles”, then check it and compare it with the examples above.

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