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2.1+2.3+2.5+2.7+2.9……4.9等于

解:按照等差数列的运算公式计算: (2.1+4.9)×29÷2=101.5 答:2.1+2.3+2.5+2.7+2.9+...+4.9等于101.5

1.1+1.2+1.3+1.4.......+2.5+2.6+2.7+2.8+2.9 2.9+2.8+2.7+2.6+……+1.5+1.4+1.3+1.2+1.1 上下相加 每一个都是4有19个4 所以 得 4x19=76 因为有两个 所以 上面的和是 76÷2=38

1.1+1.2+1.3+1.4.......+2.5+2.6+2.7+2.8+2.9 =(1.1+2.9)×(29-11+1)÷2 =4×19÷2 =38

0.1+0.3+0.5+0.7+0.9=2.5 1.1+1.3+1.5+1.7+1.9=7.5 2.1+2.3+2.5+2.7+2.9=12.5 so 2.5*10+(5+45)*9/2=250

1.1+5=6.1 1.2+4.9=6.1 1.3+4.8=6.1 ...... 共有20个6.1 6.1*20=122

1.1+1.2+1.3+1.4+1.5+1.6+1.7+1.8+1.9+2.0+2.1+2.2+2,3+2,4+2.5+2.6+2.7+2.8+2.9 可以写成(1.1+2.9)+(1,2+2.8)+(1.3+2.7)+(1.4+2.6)+(1.5+2.5)+(1.6+2.4)+(1.7+2.3)+(1.8+2.2)+(1.9+2.1)+2 =4+4+4+4+4+4+4+4+4+2 =38

1+2+3+2+1=9=3*3. 1+2+3+...+100+98+...+1=100*100=10000

1.1+1.2+1.3.......+2.0....+2.7+2.8+2.9 =(1.1+2.9)×19÷2 =4×19÷2 =2×19 =38

这道数学题无解。证明如下: 1+2+3+4+5+6+7+8=36, 设Q={1,2,3,4,5,6,7,8} 按顺序设括号内的数为a,b,c,d,e,f,g,h,a,b,c,d,e,f,g,h∈Q,a≠b≠c≠d≠e≠f≠g≠h 有(a-b)+(c+d)+(e-f)+(g+h)=1+9+2+7=19 即(a+b+c+d+e+f+g+h)-2b-2f=19 因为a+b+c+d+...

设()-(a)=1,()-(b)=2, 则:(1+2+3+...+8)-2(a+b)=1+2+9+7, ——》a+b=(36-19)/2,不是整数, 所以本题无解。

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