Definition

1. Noun:
   • Two angles whose sum is a right angle: In geometry, "complementary angles" are two angles whose measures add up to exactly 90 degrees.

Usage

• The term "complementary angles" is used as a plural noun to describe a specific relationship between two angles. It is a standard term in geometry and mathematics.
• Example: "If one angle is 30 degrees, its complementary angle is 60 degrees."
• Example: "The two acute angles in a right triangle are complementary angles."

Examples

• Noun:
  • In the diagram, angles A and B are complementary angles because their sum is 90°.
  • The teacher asked the students to identify all pairs of complementary angles on the worksheet.

Advanced Usage

• "to be complementary": This adjective form describes the relationship itself.
  • Angle X and Angle Y are complementary. (This means they are a pair of complementary angles.)
• "complement of an angle": This phrase refers to the specific angle that, when added to a given angle, equals 90 degrees.
  • The complement of a 75° angle is 15°.

Variants and Related Words

• Complement (n): The angle that completes a pair to 90 degrees. (e.g., "Find the complement of a 40° angle.")
• Complementary (adj): Describing the relationship of adding to 90 degrees. (e.g., "complementary colors" in art, though this is a different, metaphorical use from the mathematical term.)

Synonyms

• None: In the specific context of geometry, "complementary angles" is a precise technical term with no exact synonym. Descriptive phrases like "angles summing to 90 degrees" convey the same meaning.

Related Phrases

• Supplementary angles: This is a related but distinct term for two angles whose sum is 180 degrees.
  • It's important not to confuse complementary angles (sum to 90°) with supplementary angles (sum to 180°).

Noun

1. two angles whose sum is a right angle