Question 50
In circle $O,$ $G$ is a moving point on diameter $\overline{AB}.$ $\overline{AA'}$ is drawn perpendicular to $\overline{AB}$ and equal to $AG.$ $\overline{BB'}$ is drawn perpendicular to $\overline{AB},$ on the same side of diameter $\overline{AB}$ as $\overline{AA'},$ and equal to $BG.$ Let $O'$ be the midpoint of $\overline{A'B'}.$ Then, as $G$ moves from $A$ to $B,$ point $O':$