# 1-2i in Polar form?

1. Feb 7, 2013

### dylanhouse

1. The problem statement, all variables and given/known data

How do I write 1-2i in polar form?

2. Relevant equations

3. The attempt at a solution

I know r=√5, and when using x=rcosθ, I get angle of 63.43 or 296.57. However, when I take the sin inverse of-2/√5 I get -63.43. I am really confused.

2. Feb 7, 2013

### Staff: Mentor

The angle is in the 4th quadrant, so it would be either -63.43° or +296.57° (assuming your figures are correct.

3. Feb 7, 2013

### rude man

The formula is arc tan (Im part)/(Real part). You need to keep track of the numerator and denominator signs to make sure you land in the correct quadrant. In other words, the fact that the Im is - and the Re is + tells you which quadrant to land in.