JAMB 1994 · UME · Q34

What is the locus of a point $P$ which moves on one side of a straight line $XY$ so that the angle $XPY$ is always $90^\circ$ ?

Worked solution (try it first)

The angle in a semicircle is a right angle, so if $\angle XPY = 90^\circ$ then $P$ lies on the circle with $XY$ as diameter.
$P$ stays on one side of $XY$ , so it traces only half of that circle.
The locus is a semicircle, option D.