How to find corresponding angle given x coordinate of a polar graph

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Question

If we are given that $r=\theta+sin(2\theta)$ and we want to find the angle corresponding to the x coordinate of -2, how do we go about this?

i tried a couple of methods such as multiplying r on both sides to get

$r^2=r\theta+r(sin\theta)(cos\theta)$ which got me nowhere

I tried to plot the points on a graphing calculator and tried to input the value of x=-2 but my calculator was unable to find such a point like that

How should I go about this given the ability to use a conventional graphing calculator?