d = 2 (slider from -2 to 5, step 0.1)
k: x^(4) + x^(2) * y^(2) - 2 * x^(3) - 2 * x * y^(2) + (1 - d^(2)) * x^(2) + y^(2) = 0
t1: y = -sqrt(d^(2) - 1) * x
t2: -sqrt(d^(2) - 1) * x + y = 0