(x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2

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(x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2

(x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2
(x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2

(x+2y-3xy)-(-2x-y+xy),其中x+y=1/2,xy=-1/2
(x+2y-3xy)-(-2x-y+xy)
=x+2y-3xy+2x+y-xy
=(1+2)x+(2+1)y-(3+1)xy
=3x+3y-4xy
=3(x+y)-4xy
=3*1/2-4*(-1/2)
=3/2+4/2
=7/2

(x+2y-3xy)-(-2x-y+xy)
=x+2y-3xy+2x+y-xy
=3x+3y-4xy
=3(x+y)-4xy
=3/2+2
=7/2