To identify which diagram represents a step in constructing a perpendicular line that is not a perpendicular bisector, we need to understand what each of the options describes.
a. This diagram shows a vertical line segment that is perpendicular to the line segment XY and intersects it at a point that is not the midpoint, suggesting that it is constructing a perpendicular line. This fits the criteria.
b. This represents the construction of a perpendicular bisector, as it involves creating two arcs to find the midpoint (M) of AB and drawing a line through that midpoint, forming right angles with AB.
c. This diagram is ambiguous but suggests a compass is being used at point B to create an arc above the line segment. It is not clear that this forms a perpendicular line to XY.
d. This diagram indicates using the compass at point A to create an arc, again not indicating the creation of a perpendicular line.
Among these options, b clearly describes a step to construct a perpendicular bisector, while a describes a step to construct a perpendicular line. Therefore, the answer is that a is the step representing a perpendicular line that is not a perpendicular bisector.
The correct option that illustrates a construction of a perpendicular line (not a bisector) is a.