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)

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