(-1/3xy)∧2*[3xy(2x-y)-3x(2xy-4y∧2)]
解得：
1/9x*x*y*y*[3xy(2x-y)-6xy(x-2y)]
==（1/9x*x*y*y*)*3xy*[2x-y-2（x+2y)]
==(1/9x*x*y*y*)*3xy*(2x-y-2x+4y)
==(1/3xy)*3y
==1/x