[ Eq(Derivative(x1, t), k3 - (k2 + k1*x2)*x1),
  Eq(Derivative(x2, t), x3*k4*x1**2/(k5 + x1**2) - k6*x2),
  Eq(Derivative(x3, t), ((-k7) + k8*x1 - k9*x1**2)*x3) ]