Z= -3 - 8i Find the angle θtheta (in degrees) that z makes in the complex plane. Round your answer, if necessary, to the nearest tenth. Express θtheta between -180 180 degrees.

The angle is negative to indicate a clockwise rotation.

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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.

1. 3

2. 4

3. 1

hope this ! have a great day.

-wfz