In this video, you will learn how to determine the number of common tangents to two circles.

In the first diagram, we have one circle with another circle inside of it, tangent to it. These are known as internally tangent circles. These circles have only one tangent line in common.

In the next diagram, we have two circles tangent to each other, but they are outside of each other. These are known as externally tangent circles. These circles have three tangent lines in common.

In the next diagram, we have two circles that overlap. These are known as overlapping circles. These circles have **two** tangent lines in common.

In the next diagram, we have two circles that don’t touch each other. These are known as non-touching circles. These have the most number of tangent lines in common. These circles have four tangent lines in common.