**Tangent Circles**

Two circles of non-equal radius, both in the same plane, are said to be tangent to each other if they meet at only one point. Equivalently, two circles, with radii of *r _{i}* and centers at (

*x*,

_{i}*y*), for

_{i}*i*= 1, 2 are said to be tangent to each other if

- Two circles are
**externally tangent**if the distance between their centres is equal to the sum of their radii.

- Two circles are
**internally tangent**if the distance between their centres is equal to the difference between their radii.

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