7-4 Reference Angles

Today we are going to learn how to find a reference angle. This is done by using 3 simple steps.

Steps:

1. Find the original quadrant and sketch.

2. Determine if the angle is positive or negative using unit circle methods.

3. Subtract 360º or 180º until the absolute value of ø is between 0 and 90º

Now I am going to show you an example of how this is done.

Find a reference angle for Sin(355º)

1. Sin(355º) is in quadrant 4 because it is between 270º and 360º.

2. Because we are trying to find a reference angle for sin, you use the formula y/r to determine whether or not it's going to be negative or positive.

335º is in Quadrant 4, so you use the formula y/r to find out whether or not it's negative.Y is negative because you're in quadrant 4 and r is always 1, so negative/1=negative.

3. 355º-360º=|-5º|

This means that Sin(355º)= -Sin(5º)

Your final answer will be written as Sin 355º= -Sin 5º

----Carley(: