Cofunction Identities

Till now you might have found that trigonometric identities are somehow inter-related. For example, if you check

and

graphs, they are related to each other. Another example is at

, both

and

have the same values, does that mean that at every angle, they have some kind of relation? The answer is yes! And that is why this lesson focuses on cofunction identities. Let's say, your teacher asked you to find the value of

when

is at angle

, if you know cofunction trigonometric identities then this will be a piece of cake for you. Before we list the cofunction identities, you should know that two angles are complementary if the sum is

or

radians.

Let's come back to our case, so you need to find the value of

when when

is at angle

. Now you know that

hence:

This is possible with other trigonometric ratios as well, for example: