数学题……555{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y

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数学题……555
{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²÷(-4x),x=-2.y=-1

楼上的全错,
{(3x+y)(3x-y)-(x-5y)(5x-y)-(x-2y)²}÷(-4x)
={9X²-(5x²-xy-25x²+5y²)-(x²-4xy+4y²)}÷(-4x)
={9X²-5x²+xy+25x²-5y²-x²+4xy-4y²}÷(-4x)
=(28x²-9y²+5xy)÷(-4x) 把x=-2.y=-1
代入 =(28X4-9X1+5X2)÷(8)
=14.125

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