# Evaluating Trigonometric Functions Using the Reference Angle

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In this lesson we will look at Evaluating Trigonometric Functions Using the Reference Angle.

What is The Reference Angle Theorem?
The Reference Angle Theorem states that
To find the value of a trigonometric function of any angle t:
1. Determine the function value for the associated reference angle t'.
2. Depending on the quadrant in which t lies, the answer will be either be + or -.

How to evaluate trig functions using reference angles?
1. Find the reference angle for the given angle.
2. Rewrite the original trig function with the reference angle.
3. Affix the appropriate sign to the trig function (+ or -), depending which quadrant the angle terminates in.
4. Evaluate the trig function.

Evaluating Trigonometric Functions Using Reference Angles
Evaluating Trigonometric Functions Using the Reference Angle, Example 1
A quick review of the unit circle in quadrant 1 and discuss how to use the reference angle to evaluate some trig functions

Evaluating Trigonometric Functions Using the Reference Angle, Example 2
Discuss how to use the reference angle to evaluate some more trig functions.
Evaluating Trig functions using reference angles

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