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"):

$\sin(\frac{\pi}{2} - A) = \cos(A)$

$\cos(\frac{\pi}{2} - A) = \sin(A)$

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

$\sec(\frac{\pi}{2} - A) = \csc(A)$

$\csc(\frac{\pi}{2} - A) = \sec(A)$

$\tan(\frac{\pi}{2} - A) = \cot(A)$

$\cot(\frac{\pi}{2} - A) = \tan(A)$

[edit] See also

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