# Definition 2

A straight line is said to *touch* a circle which, meeting the circle and being produced, does not cut the circle.

# Definition 3

Circles are said to *touch* one another which meet one another but do not cut one another.

## Guide

Consider circle *BCD* in the figure. The line *EF* touches this circle at the point *C.* Another expression for the same thing is that *EF* is tangent to the circle at *C.*

Two circles can touch each other either internally or externally. Circle *HKL* touches circle *BCD* externally, while circle *DMN* touches circle *BCD* internally.