Question

I am leaning pre-cal right now and I don't understand it. I did arctan (3/-5) but got it wrong, how do you do this?

Answer 1

9514 1404 393

Answer:

  149.04°

Step-by-step explanation:

You must consider the signs of the components of the vector. The value -5+3i will be in the 2nd quadrant of the complex plane.

When you use the single-argument arctan function, it will tell you the angle is -30.96°, a 4th-quadrant angle. (arctan( ) is only capable of giving you 1st- or 4th-quadrant angles.)

You find the 2nd-quadrant angle by adding 180° to this value:

  -30.96° +180° = 149.04° = arg(-5+3i)

__

The attachments show the calculation using a suitable calculator (1st) and a spreadsheet (2nd). The spreadsheet function ATAN2(x,y) gives the 4-quadrant angle in radians, considering the signs of the two arguments. Here, we converted it to degrees. The calculator can be set to either degrees or radians.