If three circles 
, 
, and 
are taken in pairs, the external similarity
points of the three pairs lie on a straight line. Similarly,
the external similarity point of one pair and
the two internal similarity points of the other
two pairs lie upon a straight line, forming a similarity
axis of the three circles.
d'Alembert's Theorem
See also
Similarity PointExplore with Wolfram|Alpha
References
Dörrie, H. 100 Great Problems of Elementary Mathematics: Their History and Solutions. New York: Dover, p. 155, 1965.Cite this as:
Weisstein, Eric W. "d'Alembert's Theorem." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/dAlembertsTheorem.html