Given two parallel lines r and r′ and a point P on the plane that contains them and that is not on them, determine an equilateral triangle whose vertex is point P , and the other two, one on each of the two lines.
https://cdn.artofproblemsolving.com/attachments/9/3/1d475eb3e9a8a48f4a85a2a311e1bda978e740.png geometryconstructionEquilateral