cardioide, forma parametrica

x = a*(2 cos(t)-cos(2t))
y = a*(2 sin(t)-sin(2t))

applico curva[exp1,exp2, var, inizio, fine]

curva[a*(2*cos(t)-cos(2t)), a*(2*sin(t)-sin(2t)),t,0,6.28]

a = CurveCartesian((2 * cos(t) - cos(2 * t)), (2 * sin(t) - sin(2 * t)), t, 0, 6.28)
b = CurveCartesian(2 * (2 * cos(t) - cos(2 * t)), 2 * (2 * sin(t) - sin(2 * t)), t, 0, 6.28)