x1=2/3*(19+3*33^(1/2))^(1/3)+8/3/(19+3*33^(1/2))^(1/3)-4/3
x2=-1/3*(19+3*33^(1/2))^(1/3)-4/3/(19+3*33^(1/2))^(1/3)-4/3+i*3^(1/2)*(1/3*(19+3*33^(1/2))^(1/3)-4/3/(19+3*33^(1/2))^(1/3))
x3=-1/3*(19+3*33^(1/2))^(1/3)-4/3/(19+3*33^(1/2))^(1/3)-4/3-i*3^(1/2)*(1/3*(19+3*33^(1/2))^(1/3)-4/3/(19+3*33^(1/2))^(1/3))