### Hellenica World

The quadrifolium is a type of rose curve with n=2. It has polar equation:

r = acos(2θ),

with corresponding algebraic equation

(x2 + y2)3 = a2(x2 − y2)2

Rotated by 45°, this becomes

r = asin(2θ)

with corresponding algebraic equation

(x2 + y2)3 = 4ax2y2 .

In either form, it is a plane algebraic curve of genus zero.