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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