Answer
$$ x^2+y^2=6x$$
Work Step by Step
We know the following:
$$r=\sqrt{x^2+y^2} \\ cos\theta = \frac{x}{\sqrt{x^2+y^2} } $$
Thus:
$$\sqrt{x^2+y^2} = \frac{6x}{\sqrt{x^2+y^2} } \\ x^2+y^2=6x$$
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.