先化简,再求值3(-4X+y)(x-Y)+2(3X-2y)(x+3y),其中x=-2,y=1

问题描述:

先化简,再求值3(-4X+y)(x-Y)+2(3X-2y)(x+3y),其中x=-2,y=1

3(-4x+y)(x-y)+2(3x-2y)(x+3y)
=3(-4x²+5xy-y²)+2(3x²+7xy-6y²)
=-12x²+15xy-3y²+6x²+15xy-12y²
=-6x²+30xy-15y²
=-6×(-2)²+30×(-2)×1-15×1²
=-24-60-15
=-99
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