You can put this solution on YOUR website!
In a right triangle, the two acute angles are complementary,
meaning that their measures add up to
The way sine and cosine were defined based on a right triangle,
sine of an angle is the cosine of the complement.
(It works if you define sine and cosine based on the unit circle too).
Something similar happens with tangent and cotangent,
and with secant and cosecant.
For all the trigonometric functions the function of an angle
equals the cofunction of the complement.
Those are the cofunction identities.
Also , since
Putting it all together: