1.先化简再求值.

问题描述:

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=4
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?

[(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^...