"Compute Arg(1+2i) x Arg(2+3i)"
So:
I keep getting -60 degrees, but it should be something like 100 degrees. What am I doing wrong?
-4 + 7i lies in the second quadrant. So you want the angle lying in the second quadrant such that . It is not a 'special angle' so you will have to use your calculator and get a decimal approximation.
But this is not the answer to the question as posted. The answer to the question you've posted is .