xy=4 x-y=-7.5 则3（xy-2/3y)-1/2(2x=4xy)-(-2x-y)
问题描述：
xy=4 x-y=-7.5 则3（xy-2/3y)-1/2(2x=4xy)-(-2x-y)
答
xy=4,x-y=-7.5
x-4/x=-15/2
x^2+15/2*x-4=0
2x^2+15x-8=0
(2x-1)(x+8)=0
x=1/2或x=-8
y=8或y=-1/2
式子有点看不懂，只好自己核算了
答
原题应该为3（xy-2/3y)-1/2(2x+4xy)-(-2x-y)
=3xy-2y-x+2xy+2x+y
=5xy+x-y
=20-7.5
=12.5