## anonymous 4 years ago What are the polar coordinates for the point (1,-2) i got r = 5 but theta = arctan -2?

1. anonymous

$r=\sqrt{5}$

2. anonymous

yeah i got that far

3. anonymous

and yes, in this case $\theta =\tan^{-1}(-2)$ because you are in quadrant 4

4. anonymous

okay so arctan(-2) is correct?

5. anonymous

yes. it is always the case that $\tan(\theta)=\frac{b}{a}$ but it is not always the case that $\theta=\tan^{-1}(\frac{b}{a})$

6. anonymous

because arctan only returns answers in $[-\frac{\pi}{2},\frac{\pi}{2}]$so you need to be careful about what quadrant you are in