Which tool(s) are needed to construct a perpendicular bisector of a line segment?

You need a straight edge and a compass.

Step-by-step explanation:

The straight edge should not be marked in any way. You are not allowed to put a mark on the straight edge at all. The only property it has is that it has no curvature in any direction.

The compass must be flexible and at the same time it must be able to stay at one radius unless changed by the owner. It's only property is that it can draw a perfect  circle once the radius of the circle has been chosen,

one that is bigger than 3 1/2

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step-by-step explanatio89