Two curves are tangent externally at a point if they lie on opposite sides of their common tangent at
Tangent Externally
See also
Tangent InternallyExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Tangent Externally." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/TangentExternally.html