x+1 x x x+1 3 x 2 - 3 x 2 = 216 ____________________________ x x x x 3 x 3 x 2 - 2x3 x 2=216 ___________________________ x x 3x 6 - 2 x 6 = 216 _______________________________ x 6 = 216 ________________________________ x=3 (1/x)的-x次方的值=27