x^2 + xy + y^2 = 1
x^2/4 + xy + y^2 = 1- 3x^2/4
(x/2 + y)^2 = 1- 3x^2/4
x/2 + y = ±√(4 - 3x^2) / 2
y = - x/2 ± √(4 - 3x^2) / 2