A perpendicular bisector of a line segment 'l' is a line that is perpendicular to the line segment 'l' and cuts the line segment 'l' into two equal parts.
Given:
1. A triangle WXY.
2. A perpendicular bisector from vertex W that intersects XY at point Z.
Conclusion based on the drawing:
a. Z is the midpoint of the line segment XY because point Z lies on the perpendicular bisector of XY.