数学题;快点;有急用~~~~这几道题;快帮我想想;我等着急用~~~我会追加赏分的;~~~谢谢拉~~~Ⅰ分解因式①m2 -

4个回答

  • 1.= (m+n)(m-n)-mn(m+n) = (m+n)(m-n-mn)

    2.= x^2-2xy+y^2+3x^2-3y^2-4x^2-4y^2

    = -2xy -6y^2

    = -2y(x+3y)

    3.= y^2-5y+6 + y^2+7xy+10x^2 -(4x^2+8x+4)

    = (y-2)(y-3) + (y+5x)(y+2x) -4(x+1)^2

    这已经分解到头了……已经是最佳形式了.

    II

    (a+1)(b+1)(c+1) = abc+ab+ac+bc+a+b+c+1

    ab+a+b=bc+b+c=ac+a+c=3

    ab+a+b-(bc+b+c) = b(a-c)+(a-c) = (b+1)(a-c)=0

    同理

    (a+1)(b-c) =0

    (c+1)(a-b) = 0

    a,b,c为正数,

    于是有a=b=c,代入得到a=b=c=1或-3

    因此a=b=c=1或者a=b=c=-3 正数,所以a=b=c=1

    因此 (a+1)(b+1)(c+1) = 2x2x2 = 8