Cofunction
In mathematics, a function f is cofunction of a function g if f = g whenever A and B are complementary angles. This definition typically applies to trigonometric functions. The prefix "co-" can be found already in Edmund Gunter's Canon triangulorum.
For example, sine and cosine are cofunctions of each other :
The same is true of secant and cosecant as well as of tangent and cotangent :
These equations are also known as the cofunction identities.
This also holds true for the versine and coversine, the vercosine and covercosine, the haversine and hacoversine, the havercosine and hacovercosine, as well as the exsecant and excosecant :
