Cofunction

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.

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.

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):