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Sine and cosine are each other's cofunctions.

In mathematics, a function f is cofunction of a function g if f(A) = g(B) whenever A and B are complementary angles. This definition typically applies to trigonometric functions.[1]

For example, sine and cosine are cofunctions of each other (hence the "co" in "cosine"):

The same is true of secant and cosecant and of tangent and cotangent:

These equations are also known as the cofunction identities.[1]

This also holds true for the coversine (coversed sine, cvs), covercosine (coversed cosine, cvc), hacoversine (half-coversed sine, hcv), hacovercosine (half-coversed cosine, hcc) and excosecant (exterior cosecant, exc):

See also[edit]


  1. ^ a b Aufmann, Richard; Nation, Richard (2014), Algebra and Trigonometry (8th ed.), Cengage Learning, p. 528, ISBN 9781285965833 .