Answer: -110.6 degrees approximately
The angle is negative to indicate a clockwise rotation.
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Step-by-step explanation:
Z = -3 - 8i is in the form z = a+bi with a = -3 and b = -8
In the complex plane the point (a,b) represents the location of z = a+bi
Define three points with the locations
P = (a,b) = (-3,8)
Q = (0,0)
R = (10,0)
The angle PQR is the angle theta we're looking for. This is the angle formed between the positive x axis and the terminal point (a,b)
Use the arctan function to find theta
theta = arctan(b/a)
theta = arctan( (-8)/(-3) )
theta = 69.4439547804166
theta = 69.4 degrees approximately
Note how this theta value is in quadrant Q1, but (a,b) = (-3, -8) is in Q3
So we need to add 180 degrees to adjust this error.
69.4+180 = 249.4
and we're now in the proper quadrant. We would stop here if your teacher did not put the restriction that theta must be between -180 and 180.
However, this restriction is in place so we need to find the difference of 360 and 249.4 to get 360-249.4 = 110.6
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The angle 249.4 degrees is coterminal to -110.6 degrees. They both point in the same direction.
angle 249.4 degrees is found by starting pointing directly east and rotating 249.4 degrees counterclockwise
angle -110.6 degrees is found by starting directly east and rotating 110.6 degrees clockwise.
Check out the diagram below. I used GeoGebra to make the diagram.