八年级数学题8(x2-2y2)-x(7x+6y)+(x+3y)2,其中x=√5,y=√2

初二数学题1.(x^2+xy+y

(x^2+xy+y^2)^2-4xy(x^2+y^2) =[(x^2+y^2)+xy]^2-4xy(x^2+y^2) =(x^2+y^2)^2+2xy(x^2+y^2)+(xy)^2-4xy(x^2+y^2) =(x^2+y^2)^2-2xy(x^2+y^2)+(xy)^2 =(x^2-xy+y^2)^2 －－－－－－－－－－－－－－－ 5(2a-1)(a-2)-3(2-a)^2 =(a-2)[5(2a-1)-3(a-2)] =(a-2)(10a-5-3a+6) =(a-2)(7a+1) －－－－－－－－－－－－－－－ 已知x+y-2=0,求(x^2-y^2)^2-8(x^2+y^2)的值...全部

  (x^2+xy+y^2)^2-4xy(x^2+y^2) =[(x^2+y^2)+xy]^2-4xy(x^2+y^2) =(x^2+y^2)^2+2xy(x^2+y^2)+(xy)^2-4xy(x^2+y^2) =(x^2+y^2)^2-2xy(x^2+y^2)+(xy)^2 =(x^2-xy+y^2)^2 －－－－－－－－－－－－－－－ 5(2a-1)(a-2)-3(2-a)^2 =(a-2)[5(2a-1)-3(a-2)] =(a-2)(10a-5-3a+6) =(a-2)(7a+1) －－－－－－－－－－－－－－－ 已知x+y-2=0,求(x^2-y^2)^2-8(x^2+y^2)的值 (x^2-y^2)^2-8(x^2+y^2) =[(x-y)(x+y)]^2-8(x^2+y^2) =[(x-y)^2][(x+y)]^2-8(x^2+y^2) =4(x-y)^2-8(x^2+y^2) =-4(x+y)^2 =-4*2*2 =-16 －－－－－－－－－－－－－－－－－ a^3-5a+4 =(a^3-a)-(4a-4) =a(a^2-1)-4(a-1) =a(a-1)(a+1)-4(a-1) =(a-1)(a^2+a-4) －－－－－－－－－－－－－－－－－－ (x-y)^2+3(x^2-y^2)-4(x+y)^2 =(x-y)^2+3(x-y)(x+y)-4(x+y)^2 =[(x-y)+4(x+y)][(x-y)-(x+y)] =-2y(5x+3y) －－－－－－－－－－－－－－－－－－ 2m^2(n+2)-12mn-3n^2 =2m^2*n+4m^2-12mn-3n^2 =?。
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