2x+3y=-5/6
(2x+3y)②次幂=25/36
(2x+y)(2x-y)=4x2-y2=4*1/9-1/4=16/36-9/36=7/36
(2x+3y)②次幂-(2x+y)(2x-y)=25/36-7/36=18/36=1/2