
Bisecting an Angle
How to bisect an angle with compass and straightedge or ruler. To
bisect an angle means that we divide the angle into two equal
(congruent)
parts without actually measuring the angle. This Euclidean construction works by creating two
congruent triangles.
See the proof below for more on this.
Printable stepbystep instructions
The above animation is available as a
printable stepbystep instruction sheet, which can be used for making handouts
or when a computer is not available.
Proof
This construction works by effectively building two congruent triangles.
The image below is the final drawing above with the red lines added and points A,B,C labelled.
 Q.E.D
Try it yourself
Click here for a printable worksheet containing three angle 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.
Other constructions pages on this site
Lines
Angles
Triangles
Right triangles
Triangle Centers
Circles, Arcs and Ellipses
Polygons
NonEuclidean constructions
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