Answer:
Using trigonometric identities: A trigonometric identity is a relationship between trigonometric functions that we can use to find an exact value of a trigonmetric function.Using the unit circle: The unit circle is a circle with its center at the origin and a radius of 1 unit. If we place an angle, θ, with its initial side along the positive x-axis, then the point where the angle's terminal side intersects the unit circle is (cos(θ), sin(θ)).Using reference angles: Reference angles are the smallest angle that the terminal side of an angle makes with the x-axis. As it turns out, trigonometric functions of an angle and its reference angle have the same value, except that they may have different signs.
For example, suppose we want to find the exact value of tan(405°). First, we take a look at the angle 405° on a graph with the unit circle:
in this that the reference angle of 405° is 45°. We can use the fact that tangent is positive in the first quadrant and the rule for reference angles to deduce that tan(405°) = tan(45°). Then we can use the well-known fact that tan(45°) = 1 to get that tan(405°) = 1.
Explanation: