Consider (in the plane) three concentric circles with radii 1,2 and 3 and equilateral triangle Δ such that on each of the three circles is one vertex of Δ . Calculate the length of the side of Δ .
https://1.bp.blogspot.com/-q40dl3TSQqE/Xy1QAcno_9I/AAAAAAAAMR8/11nsSA0syNAaGb3W7weTHsNpBeGQZXnHACLcBGAsYHQ/s0/flanders%2B2013%2Bp4.png geometryconcentric circlesconcentricEquilateral