求当X=4,y=负三分之二时,代数式2(二分之一x^2-3xy-y^2)-(2x^2-7xy-2y^)

过程要清楚哦亲

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2(二分之一笑笑x^2-3xy-y^2)-(2x^2-7xy-2y^)
=x²-6xy-2y²-2x²+7xy+2y²
=-x²+xy
=-4²春神+4x(-2/3)
=-16-8/扒升亏3
=-56/3

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2(二分之一游哪稿x^2-3xy-y^2)-(2x^2-7xy-2y^)
=x²-6xy-2y-2x²+7xy+2y²
=-x²+xy
=-4²+4*(-2/3)
=-16-8/3
=-56/缓改3
=-3分神孝之56

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