Wikipedia User:TrigProj

This article will cover cofunctions. Simple examples will be given.

Cofunctions are trigonometric functions of compliments of an angle. In other words, sin θ = cos (90 - θ). This works the other way around too. example: cos θ = sin (90 - θ)

Here are two examples with numbers:

We'll use this triangle. (Use the link on the right.) The angles are 75-70-35. Theta is the bottom, right angle or the 35˚ angle.



sin 35˚ = cos (90 - 35) or 55˚

tan 35˚ = cot (90 - 35) or 55˚

Put those into a calculator. They all come up the same don't they?

Now let's move theta to the bottom left corner or the 75˚ angle.

cos 75˚ = sin (90 - 75) or 25˚

csc 75˚ = sec (90 - 75) or 25˚

Again, put them into a calculator and they should be the same. That is the essence of cofunctions.

Now two last examples with theta in the top angle or the 70˚ angle:

sec 70˚ = csc (90 - 70) or 30˚

cot 70˚ = tan (90 - 70) or 30˚