Answer
$\pm 1$
Work Step by Step
$r^{2}=-2\cos 2\theta \Rightarrow r^{2}=-2\cos \left( 2\times 60\right) =-2\cos 120=-2\times \left( -\dfrac {1}{2}\right) =1\Rightarrow r=\pm 1$
You can help us out by revising, improving and updating this answer.
Update this answerAfter you claim an answer you’ll have 24 hours to send in a draft. An editor will review the submission and either publish your submission or provide feedback.