x^2 + 1/9x-16/27=0
x^2+1/9x+ (1/18)^2 - (1/18)^2 - 16/27=0
(x+1/18)^2=1/324+16*12/324=193/324
x+1/18=(193)^(1/2)/18 (舍负)
x=[(193)^(1/2)-1]/18