计算:(x-3y)(x+7y)化简:(-4x+1)(2x+3)-(-8x)(x+1)先化简,再求值:2(x-8)(x+5)-(2x-1)(x+2),其中x=-7

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计算:(x-3y)(x+7y)化简:(-4x+1)(2x+3)-(-8x)(x+1)先化简,再求值:2(x-8)(x+5)-(2x-1)(x+2),其中x=-7
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计算:(x-3y)(x+7y)化简:(-4x+1)(2x+3)-(-8x)(x+1)先化简,再求值:2(x-8)(x+5)-(2x-1)(x+2),其中x=-7
计算:(x-3y)(x+7y)
化简:(-4x+1)(2x+3)-(-8x)(x+1)
先化简,再求值:2(x-8)(x+5)-(2x-1)(x+2),其中x=-7

计算:(x-3y)(x+7y)化简:(-4x+1)(2x+3)-(-8x)(x+1)先化简,再求值:2(x-8)(x+5)-(2x-1)(x+2),其中x=-7
1.(x-3y)(x+7y)=x^2+7xy-3xy-21y^2=x^2-21y^2+4xy
2.(-4x+1)(2x+3)-(-8x)(x+1)=-8x^2-12x+2x+3+8x^2+8x=-2x+3
3.2(x-8)(x+5)-(2x-1)(x+2)=2(x^2+5x-8x-40)-(2x^2+4x-x-2)=2x^2-6x-80-2x^2-3x+2=-9x-78,当x=-7时,原式=-9*(-7)-78=-15

1.x的平方-7y的平方+4xy
2.-2x+3
3.x^2+3x-40-2x^2+2-3x=-x^2+42,x=-7,的7

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