In geometry, **complementary angles** are angles whose measures sum to 90°. If the two complementary angles are adjacent (i.e. have a common vertex and share just one side) their non-shared sides form a right angle.

In Euclidean geometry, the two acute angles in a right triangle are complementary, because the sum of internal angles of a triangle is 180 degrees, and the right angle itself accounts for ninety degrees.

The adjective *complementary* is from Latin *complementum*, associated with the verb *complere*, "to fill up". An acute angle is "filled up" by its complement to form a right angle.

Read more about Complementary Angles: Trigonometric Ratios

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**Complementary Angles**- Trigonometric Ratios

... The sine of an

**angle**equals the cosine of its

**complementary angle**... It is therefore true that, if

**angles**A and B are

**complementary**, and ... The tangent of an

**angle**equals the cotangent of its

**complementary angle**...