Google Classroom
GeoGebraGeoGebra Classroom

Bisecting an angle

Sometimes you will be given an angle and asked to bisect it (split it into two). All you need is a ruler and compass!
To start off with, we want to find a point on AC and another on AB that are the same distance from A. We will do this with the compass tool, but first we need to set the radius. From the line drop down menu, select "Segment". Then click on two points in empty space that are about half the distance AB away from each other. This will be our radius. Next select the compass tool from the compass drop down menu. Click on the line segment you drew to set the radius for the compass, and then on point A. Geogebra will draw a circle for you with your chosen radius around A as its centre! There is a button to undo and to restart if you make a mistake.
We now have two new points F and G that are the same distance as each other from point A. If we now draw two more circles of the same radius but with centres at points F and G, we will have these intersecting at point A and at another new point. Can you visualise a line connecting our new point back to point A? Create that line using the "Segment" tool from the line drop down menu. Well done! You have successfully bisected the angle BCA. Try moving points B and C. What do you see?