Construct the Perpendicular Bisector of a Segment Using a Compass

Geometry Essentials For Dummies

To construct a perpendicular bisector of a segment, you use your compass to locate two points that are each equidistant from the segment's endpoints and then finish with your straightedge. The following example shows you how it's done.

This figure should help as you work through the construction process:

Constructing a perpendicular bisector.

Open your compass to any radius r that's more than half the length of segment CD, and construct arc (C, r).
Construct arc (D, r) intersecting arc (C, r) at points G and H.
Draw line GH. You're done: line GH is the perpendicular bisector of segment CD.

About This Article

About the book author:

Mark Ryan has more than three decades’ experience as a calculus teacher and tutor. He has a gift for mathematics and a gift for explaining it in plain English. He tutors students in all junior high and high school math courses as well as math test prep, and he’s the founder of The Math Center on Chicago’s North Shore. Ryan is the author of Calculus For Dummies, Calculus Essentials For Dummies, Geometry For Dummies, and several other math books.