How to bisect a line with compass and straightedge or ruler

Perpendicular bisector of a line segment

Geometry construction using a compass and straightedge

- Printable problem worksheet
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Click on 'Next' to go through the construction one step at a time, or click on 'Run' to let it run without stopping. (If there is no image below, see support page.)

Step-by-step Instructions

	After doing this	Your work should look like this
	Start with a line segment PQ.
1	Place the compass on one end of the line segment.
2	Set the compass width to a approximately two thirds the line length. The actual width does not matter.
3	Without changing the compass width, draw an arc above and below the line.
4	Again without changing the compass width, place the compass point on the the other end of the line. Draw an arc above and below the line so that the arcs cross the first two.
5	Using a straightedge, draw a line between the points where the arcs intersect.
6	Done. This line is perpendicular to the first line and bisects it (cuts it at the exact midpoint of the line).

Try it yourself

Click here for a printable worksheet containing three line bisection problems. When you get to the page, use the browser print command to print as many as you wish. The printed output is not copyright.

Constructions pages on this site

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Triangle Centers

Circles, Arcs and Ellipses

Non-Euclidean constructions