West Texas A&M University Reference Angle Discussion

Reference Angle

A reference angle is the acute angle formed by the terminal side of the given angle and the x-axis.

How to find the reference angle:

Step 1: Sketch the given angle

Step 2: Drop a perpendicular to the x-axis

Step 3: Determine the angle measure of the triangle formed

You can use reference angles to find the sine, cosine and tangent of non-acute angles:

To find the value of sine, cosine and tangent at non-acute angles (from 90 to 360), first draw the angle on the unit circle and find the reference angle.

A reference angle is formed by the terminal side and the x-axis and will therefore always be acute.

When evaluating sine, cosine and tangent for the reference angle, determine if each value is positive or negative by identifying the quadrant the terminal side is in.

Fig. 1

Fig. 2