Lines are defined by two points; the common tangent line to circle is also defined by two circles. If there is a tangent between multiple circles, it means that the common tangent defined by two circles is also the tangent of the multiple circles.

Steps:
1. Enter L, or click home>draw>circle
Execute the Line command
2. Enter tan, or Shift + the right mouse button, click the tangent point in the right menu, e.g. picture 1), and select the approximate position of the first tangent point.
Select the first tangent point
3. Enter tan, or Shift + the right mouse button, click the tangent point in the right mouse button, and select the approximate position of the second tangency.
Select the second tangent point.
Attention: 2 circles create 4 common tangents, 2 are external common tangents, and the other two are internal common tangents. Thus you should pay attention to the profile of the circle when selecting the tangent point. For example, in picture 2, common tangent 1 is an external one created by two profiles of the same side; common tangent 2 is an internal one created by two profiles of different sides.

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