External (or positive) and internal (or negative) similarity points of two circles with centers 
and 
and radii 
and 
are the points 
and 
on the lines 
such that
 |
or
 |
Similarity Point
See also
d'Alembert's Theorem, Homothetic Center, Similitude Center, Similitude CircleExplore with Wolfram|Alpha
Cite this as:
Weisstein, Eric W. "Similarity Point." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/SimilarityPoint.html