Question 154
For $0 \leq y \leq 2$, let $D_{y}$ be the half-disk of diameter $2$ with one vertex at $(0, y)$, the other vertex on the positive $x$-axis, and the curved boundary further from the origin than the straight boundary. Find the area of the union of $D_{y}$ for all $0 \leq y \leq 2$.