GeoGebra - Spoken Tutorials - Assignments
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Tangents to a circle in geogebra


Angle between  tangents drawn from an external point to a 
circle, is supplementary to the angle subtended by the line­segment joining the points of contact at the centre.


To verify the theorem

1.Draw a circle

2.Draw  tangents from an external point 

3.Mark points of intersection of the tangents

4.Join center of the circle to intersection points

5.Measure  angle at the center, and

7.Measure angle between the tangents 

8.What is the sum of the two angles?

9.Join center and external point

10.Does the line­segment bisect angle at the center?

11.Hint ­ Use Angle Bisector tool