§ 20:

O79
2 y₂² + (3/2)√2 (y₁+y₂) + 1 = 0 (parabola);
y₁² + 4 y₂² - (1/3)√3 y₁ + (1/3)√6 y₂ = 0 (ellipse).

O80
x₁ = 0.