7-4 Reference Angles!

So, I am going to explain how to find reference angles.

Note: Reference angles are pretty much like a reduced fraction. All reference angles must be between 0 and 90 degrees.

There are three steps in finding reference angles. These three steps are:

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1.)First you must find the original quadrant and sketch it.

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2.)The next thing you must do is find out if the angle is postitive or negative. You do this by using the unit circle method.

3.)The last step is to subtract 360 degrees or 180 degrees until the absolute value of theta is between 0 and 90 degrees.

Okay, so now I am going to do an example of finding the reference angle.

Example 1: sin(128 degrees)

1.)This would be in quadrant II because it is in between 90 and 180 degrees.

2.)Sin=y/r, so because of this your angle is going to be postitive because your y is postitive in your sketch above.

3.)128-180=-52. The absolute value of -52 is 52.

So your answer would be: sin 52 degrees.

-Halie :)