先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5
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先化简再求值(x-y)(x-2y)+(x-2y)(x-3y)-2(x-3y)(x-4y) x=4 y=5
(X-y)(x-2y)+(X-2Y)(X-3Y)-2(X-3Y)(X-4Y)
=(x-2y)(x-y+x-3y)-2(x-3y)(x-4y)
=(x-2y)(2x-4y)-2(x-3y)(x-4y)
=2x²-4xy-4xy+8y²-2(x²-4xy-3xy+12y²)
=2x²-4xy-4xy+8y²-2x²+8xy+6xy-24y²
=6xy-16y²
=6x4x5-16x5²
=120-400
=-280
再问: 确定对?
再答: 嗯哪,学习进步~
再问: thank you
再答: 满意请采纳哦~
=(x-2y)(x-y+x-3y)-2(x-3y)(x-4y)
=(x-2y)(2x-4y)-2(x-3y)(x-4y)
=2x²-4xy-4xy+8y²-2(x²-4xy-3xy+12y²)
=2x²-4xy-4xy+8y²-2x²+8xy+6xy-24y²
=6xy-16y²
=6x4x5-16x5²
=120-400
=-280
再问: 确定对?
再答: 嗯哪,学习进步~
再问: thank you
再答: 满意请采纳哦~
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