Question

先化简，再求值:(x+2y)^2-2(x-y)(x+y)+2y(x-3y),其中x=-2,y=1/2

先化简，再求值:(x+2y)^2-2(x-y)(x+y)+2y(x-3y),其中x=-2,y=1/2

Answer 1

(x+2y)^2-2(x-y)(x+y)+2y(x-3y)
=x^2+4xy+4y^2-2x^2+2y^2+2xy-6y^2----展开
=-x^2+6xy----合并同类项
=-4-6*2*1/2----代入求解
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