An Angle Bisector splits an angle into two equal parts.
To bisect a given angle, draw an arc, setting the point on the tip of the angle and cutting the two angle lines with the arc.
Keeping the compasses set to the same radius, place the point on one of the intersection points. Draw another arc, further from the point.
Repeat the process for the other intersection point. Draw this arc to cut the newest arc, to create a new point.
Draw a line from the top of the angle to this point . The angle has now been bisected.
1. Draw a line at 80º to a base line using a protractor. Bisect the angle wihout using a protractor.
Create the intersects on the original lines. Use the intersects to create a third intersect, which will provide the point for the bisector.
2. Draw a line at 80º to a base line using a protractor. Without any further use of a protractor, draw an angle of 20º.
First, bisect the angle of 80º to obtain an angle of 40º.
Repeat the process to bisect one of the 40º angles to obtain an angle of 20º.