The distance between point $P$ and the origin, $O$, is $r$ units. The line $OP$ forms an angle of $\phi$ with the $x$-axis.
Point $P'$ is the result of rotating point $P$, $\theta$ degrees counter-clockwise around the origin.
The line $AP'$ forms a right angle with line $OP$.

**If point $P$ is at $(x, y)$, $y$ is equal to the length of which line segment?**
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