A Curve called Helen!

Can you tell what curve has been called the ‘Helen of geometers?

Answer:       Cycloid. Cycloid is the simplest member of the class of curves known as roulettes and it was not known before the 15 Century. And it was seriously studied until the 17^th Century.

                  Many great mathematicians like Descartes, Pascal, Lisbuitz, the Bermoullis and others have investigated the properties of the Cycloid that it was sometimes named the ‘Helen on Geometers”.