[ Eq(x3, 2*k4*x1*k7/(k6 - k4*x1 + k5*k6 + k7*k4*x1 + ((k6 - k4*x1 + k5*k6 + k7*k4*x1)**2 - 4*(k6 - k4*x1)*k4*x1*k7)**(1/2))),
  Eq(x4, k8 - x3) ]