Till now you might have found that trigonometric identities are somehow inter-related. For example, if you check $\text{[math]}$ and $\text{[math]}$ graphs, they are related to each other. Another example is at $\text{[math]}$ , both $\text{[math]}$ and $\text{[math]}$ 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 $\text{[math]}$ when $\text{[math]}$ is at angle $\text{[math]}$ , 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 $\text{[math]}$ or $\text{[math]}$ radians.

$\text{[math]}$ $\text{[math]}$ $\text{[math]}$

Let's come back to our case, so you need to find the value of $\text{[math]}$ when when $\text{[math]}$ is at angle $\text{[math]}$ . Now you know that $\text{[math]}$ hence:

$\text{[math]}$

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

$\text{[math]}$ $\text{[math]}$

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Emma

I am passionate about travelling and currently live and work in Paris. I like to spend my time reading, gardening, running, learning languages and exploring new places.

Cofunction Identities

Trigonometric Values

Trigonometric Identities

Trigonometric Ratios

Trigonometric Functions

Trigonometric Formulas

Systems of Simultaneous Trigonometric Equations

Unit Circle

Sine and Cosine Law

Solving Right Triangles

Even-Odd Identities

Oblique Triangles

Pythagorean Identities

Measurement of Angles

Other Trigonometric Identities

Trigonometric Equations