[ Diff(x[1], t) = 0,
  Diff(x[2], t) = (1*k[3]*k[4]/(1 + (x[3]*(1 - 2/(1 + (1 + 8*k[6]*x[3])^(1/2)))/(2*k[5]))^2) + (-1)*k[8]*x[2]*k[3])/k[3],
  Diff(x[3], t) = (1*k[7]*x[2]*k[3] + (-1)*k[9]*x[3]*k[3] + (-1)*k[3]*(k[10]*x[3]*2/(1 + (1 + 8*k[13]*x[3])^(1/2)) + k[11]*x[3])/(k[12] + x[3]))/k[3] ]