Intersection between two circles
From NewMarsWiki
Application in orbital Mechanics
For a given value d for a transfer obit which is the sum of the distance for each foci to a point on the ellipse of the transfer orbit, it can be shown that the second foci is the intersection of a circle centered at the departure point (e.g. Earth) and an intersection of a circle centered at the arrival point (e.g. Mars)
External Links
Intersection between two circles from [mathworld].