Click on the blue points and drag them to change the figure.
What can you say about the circles if they have only two common tangents? What can you say about the circles if they have four common tangents?
 Manipulative 1  Common Tangents of Two Circles Created with GeoGebra. 

Each pair of
circles
in a
plane
have zero, two or four
tangent lines in common. If one of the circles is completely
contained within the other, they have no common tangents. If the circles intersect, they have
two tangent lines in common. If the circles do not intersect and one is not contained
by the other, they have four tangent lines in common. These tangent lines are called the
common tangents of the circles.
