Meaning & use
complementary angle
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Meaning
nouncountablemathematics
Either of two angles whose sizes together equal exactly ninety degrees, which is a right angle.
Grammar: Usually used in the plural or as a pair: two complementary angles, or one angle is the complement of the other.
Patterns
- complementary angle of something
- complementary angle to something
A thirty degree angle and a sixty degree angle are complementary angles.
If one complementary angle measures forty degrees, the other must measure fifty.
The two acute angles in a right triangle are complementary angles.
Word forms
| plural | complementary angles |
|---|
Common combinations
- find the complementary angle
- Find the complementary angle by subtracting from ninety.
- pair of complementary angles
- A pair of complementary angles forms a right angle when placed together.
- complementary angle of fifty degrees
- The complementary angle of fifty degrees is forty degrees.
- two complementary angles
- Two complementary angles never include an obtuse angle.
- adjacent complementary angles
- Adjacent complementary angles share one side and form a corner.
Synonyms and how they differ
- complement
- It is the short form used when one angle is described in terms of the other, as in the complement of thirty degrees.
Opposites
Word family
- complement noun
- the angle that adds to another to make ninety degrees
- complementary adjective
- adding to or completing something
- angle noun
- the space between two lines that meet
- supplementary angle noun
- an angle that adds to another to make 180 degrees
Commonly confused: complementary angle or supplementary angle? complementary angle or complimentary?
complementary angle vs supplementary angle
Supplementary angles add up to 180 degrees. Complementary angles add up to 90 degrees.
complementary angle vs complimentary
Complimentary means praising or free of charge. The mathematical word is complementary, spelled with an e.
Practice
One of two complementary angles measures 35 degrees. What does the other measure?
Choose one answer.
Complementary angles add up to 90 degrees, so 90 minus 35 is 55. The 145 degree choice is the supplementary angle, which is the tempting mistake.
Make it your own
Write a sentence using “complementary angle”, then check it and compare it with the examples above.