second tangency principle

Two circles can share two points, one or none.

When they share one, they are said to be tangent,

and the shared point is called the point of tangency. 

There are two situations in which two circles share a point: 

• CASE 1. Neither circle contains the other.
• CASE. One circle contains the other. 

SECOND TANGENCY PRINCIPLE

When two circles are tangent, their centres

and the point of tangency are aligned.