Bisect an Angle

Angle Bisector
An angle bisector is a line or ray that divides an angle into two equal parts.

The following figures give the steps to construct an angle bisector. Scroll down the page for more examples and solutions.

 

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Steps to Construct an Angle Bisector
Given: Angle AOB (with point O as the vertex).

1. Draw an Arc
   Place the compass on the vertex O and draw an arc that crosses both arms (OA and OB).
   Label the points where the arc intersects the arms as C and D.
   
2. Draw Two More Arcs
   Place the compass on point C and draw an arc inside the angle.
   Without changing the compass width, place it on point D and draw another arc so that it intersects the first arc.
   Label the intersection point E.
   
3. Draw the Angle Bisector
   Use a ruler to draw a straight line from vertex O through point E.
   The line OE is the angle bisector splitting ∠AOB into two equal angles.
   

Videos

Construct an Angle Bisector
An angle is formed by two rays with a common endpoint. The angle bisector is a ray or line segment that bisects the angle, creating two congruent angles. To construct an angle bisector you need a compass and straightedge.

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Bisecting an Angle
Using compass and straight edge to bisect an angle.

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Bisect an Angle

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Bisect an Angle
Shows how to bisect a given angle using only a compass and straightedge.

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