This week I'm going to do a review on how to find reference angles. Reference angles are kind of like reduced fractions in that they must always be between 0 and 90. There are a few simple steps in finding a reference angle:
1) Find the original quadrant and sketch.
2) Determine if the angle is positive or negative using your unit circle methods.
3) Subtract 360 or 180 until the absolute value of "theta" is between 0 and 90.
Example 1: Find a reference angle for sin 128
- It's in quadrant 2, where sin is positive, which means the reference angle will be positive.
- 128 - 180 = -52; I make 52 positive.
- final answer = sin 52
Example 2: Evaluate cos 45
- All I have to do is go to my trig chart and find the value of cos 45.
- = sq root of 2/2
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