JAMB 2003 · UME · Q24

The locus of a point $P$ which moves on one side only of a straight line $XY$ so that $\angle XPY = 90^\circ$ is

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 diameter $XY$ .
$P$ stays on one side of $XY$ , so it traces only half of that circle: a semicircle, option C.