In other words, with only the angle θ, we can say that the corresponding point
on the unit circle is simply cosθ, sinθ. This helps us solve difficult-looking
problems, like the following.
In the unit circle to the left, which of the following is equal to c?
A) sinθ
B) cosθ
C) tanθ
D) secθ
Because they are asking about the x-coordinate, we know that we are looking
for cos(θ), so our answer is B.
Additionally, the unit circle helps you find the values of trigonometric
functions within each quadrant of the graph.