Problem

Source: IMO LongList 1982 - P25

Tags: geometry, circles, tangency, euclidean distance, IMO Shortlist, IMO Longlist



Four distinct circles $C,C_1, C_2$, C3 and a line L are given in the plane such that $C$ and $L$ are disjoint and each of the circles $C_1, C_2, C_3$ touches the other two, as well as $C$ and $L$. Assuming the radius of $C$ to be $1$, determine the distance between its center and $L.$