1.先化简再求值.[(x+1/2y)^2+(x-1/2y)^2](2x^2-1/2y^2),其中x=-3,y=42.小明
2个回答

[(x+1/2y)^2+(x-1/2y)^2](2x^2-1/2y^2),其中x=-3,y=4

[(x+1/2y)^2+(x-1/2y)^2](2x^2-1/2y^2)

=(x^2+xy+1/4y^2+x^2-xy+1/4y^2)(2x^2-1/2y^2)

=(2x^2+1/2y^2)(2x^2-1/2y^2)

=4x^4-1/4y^4

当x=-3,y=4时

原式=4*(-3)^4-1/4*4^4

=324-64

=260

2.小明在化简A-(ab+2bc-4ac)时,由于马虎,将"A-"写成"A+",得到的结果是3ab-2ac+5bc,问:正确的结果是多少?

A+(ab+2bc-4ac)=3ab-2ac+5bc

A=2ab+2ac+3bc

所以

A-(ab+2bc-4ac)

=2ab+2ac+3bc-ab-2bc+4ac

=ab+6ac+bc

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