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Mathematics 18 Online
OpenStudy (anonymous):

How to get angle from -120-35i?

OpenStudy (anonymous):

I thought it was atan(35/120) but why is the answer -163.73? Seems like they subtract atan(-35/-12) by 180.. Any rules I am not aware of it

OpenStudy (mathstudent55):

This is a third quadrant angle. Since the inverse tangent of a positive number gives you the reference angle in the first quadrant, you must then calculate what that angle will be in the third quadrant by either adding or subtracting 180 degrees.

OpenStudy (anonymous):

But then should that not be +180?

OpenStudy (mathstudent55):

What do you get for atan(35/120)?

OpenStudy (anonymous):

16.26

OpenStudy (anonymous):

Do you know why we're looking for this angle oppose to the other one?

OpenStudy (anonymous):

|dw:1361074794122:dw|

OpenStudy (mathstudent55):

|dw:1361074770992:dw| Angle alph is the reference angle and it does measure 16.26... degrees.

OpenStudy (anonymous):

ahh I'm kind of confused

OpenStudy (anonymous):

Don't get why they subtracted 180

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