2x·[(1/2x)²-1] - 3x·[（1/3x)²+2/3]
=[1/(2x)²·2x - 1·2x] - [1/(3x)²·3x + 2/3·3x]
=1/2x - 2x - 1/3x - 2x
=(3-2)/6x - 4x
=1/6x - 4x