lemniscata di bernoulli: parametrica

a =2 modificabile

x = (a*sin(t))/(1+cost()^2)

y = (a*sin(t)*cos(t)) / ( 1+ cos(t)^2)

a = 1.9 (slider from -5 to 5, step 0.1)
b = CurveCartesian(a * sin(t) / (1 + cos(t)^(2)), a * sin(t) * cos(t) / (1 + cos(t)^(2)), t, 0, 6.28)