What are the polar coordinates of (1,-2) and how do you find them?

[Jbreezy]

Homework Statement

Convert (1,-2) to polar coordinates find one representation with r >0 and one with r <0. Also 0<= theta <= 2 PI

Homework Equations

I used tantheta = y /x , and x^2 +y^2 = r^2

The Attempt at a Solution

I got (sqrt(5) , arctan(-2)) , (-sqrt(5) , arctan(-2) + pi )
Is this OK?

 

[SteamKing]

Does arctan(-2) satisfy 0 <= theta <= 2 pi?

 

[Jbreezy]

I think so it is -63.43 degrees in my calculator and I forget how arctan comes back in the calculator but if I add 180 to that it is still only 116. I forget where is comes back to the domain on the calculator I mean.

 

[Mark44]

But -63.43° is not in the interval [0°, 360°]. That was essentially what SteamKing was objecting to.

 

[Jbreezy]

OH opps. OK so add 360 to it. Then I'm good right?