快,明天要交(2x-y)(x+y)-2(x+y)²+3xy,y=1/6

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快,明天要交(2x-y)(x+y)-2(x+y)²+3xy,y=1/6
快,明天要交(2x-y)(x+y)-2(x+y)²+3xy,y=1/6

快,明天要交(2x-y)(x+y)-2(x+y)²+3xy,y=1/6
(2x-y)(x+y)-2(x+y)²+3xy
=2x²+2xy-xy-y²-2(x²+2xy+y²)+3xy
=2x²+2xy-xy-y²-2x²-4xy-2y²+3xy
=-3y²
当y=1/6时原式=-3*1/36=-1/12

原式=2x²+xy-y²-2x²-4xy-2y²+3xy
=-3y²
=-3x1/6²
=-1/12

原式=2x²+xy-y²-2x²-4xy-2y²+3xy
=-3y²

(2x-y)(x+y)-2(x+y)²+3xy
=(x+y)(2x-y-2x-2y)+3xy
=-3xy-3y²+3xy
=-3y²
=-1/12