1.试比较代数式3x?-2x+7与4x?-2x+7的大小。-爱科技问答

1.试比较代数式3x?-2x+7与4x?-2x+7的大小。

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13643349600WHD

两者做差，后者减前者得x?.而x?≥0恒成立，所以后者≥前者
098765

奥数啊.使用计算器.
yangyanjun1994

1x1/2+1/2x1/3+1/3x1/4+1/4x1/5+1/5x1/6+1/6x1/7
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6+1/9-1/7
=1-1/7
=6/7
276424991

2-1/4-1/3+1/2+1/2x1/7
=1-1/3+1/5+1/6-1/3x1/4+1/6+1/4x1/6x1/5x1/2+1/6+1/3-1/4+1/5+1/5-1/7
=1-1/7
=6ǘx1/
806321325

先去括号，然后合并同类项原式=3x?-x?-（6x?-7x）-2x?+4x?+8x =3x?-x?-6x?+7x-2x?+4x?+8x =-2x?+15x 将x=-1带入得到原式=-17
MZ

1x1/2 1/2x1/3 1/3x1/4 1/4x1/5 1/5x1/6 1/6x1/7 1/7x1/8 中间是+号? =1-1/2+1/2-1/3+1/3-1/4+.1/4-1/5+1/5-1/6+1/6-1/7+1/7-1/8 =1-1/8=7/8

1.试比较代数式3x?-2x+7与4x?-2x+7的大小。