1+1+2+1+2+3+1+2+3+4+1+2+3+4+5+"""""""(省略号)1+2+3+""""""'+n=?
来源:学生作业帮 编辑:作业帮 分类:数学作业 时间:2024/10/04 05:15:37
1+1+2+1+2+3+1+2+3+4+1+2+3+4+5+"""""""(省略号)1+2+3+""""""'+n=?
=n*1+(n-1)*2+(n-2)*3+.+(n-(n-1))*n
=(1+2+3+...+n)*n-(1*2+2*3+3*4+...+(n-1)*n)
=n^2(n+1)/2-((1^2-1)+(2^2-2)+(3^2-3)+……+(n^2-n))
=n^2(n+1)/2-((1^2+2^2+3^2+……+n^2)-(1+2+3+……+n))
= n^2(n+1)/2-(n(n+1)(2n+1)/6-n(n+1)/2)
=n^2(n+1)/2-n(n+1)(2n+1)/6+n(n+1)/2
=(n+1)(3n^2-2n^2-n+3n)/6
=(n+1)(n^2+2n)/6
=n(n+1)(n+2)/6
=(1+2+3+...+n)*n-(1*2+2*3+3*4+...+(n-1)*n)
=n^2(n+1)/2-((1^2-1)+(2^2-2)+(3^2-3)+……+(n^2-n))
=n^2(n+1)/2-((1^2+2^2+3^2+……+n^2)-(1+2+3+……+n))
= n^2(n+1)/2-(n(n+1)(2n+1)/6-n(n+1)/2)
=n^2(n+1)/2-n(n+1)(2n+1)/6+n(n+1)/2
=(n+1)(3n^2-2n^2-n+3n)/6
=(n+1)(n^2+2n)/6
=n(n+1)(n+2)/6
S=(1/1x3)+(1/3x5)+省略号+1/(2n-1)(2n+1)
计算(1+3+5+7+省略号+99+101)-(2+4+6+8+省略号+98+100)的结果是( )
1+2+2的2次方+2的3次方+省略号+2的n次方=?
1/1+2+1/1+2+3+1/1+2+3+4+省略号+1/1+2+省略号+99
1+1+2+1+2+3+1+2+3+4+1+2+3+4+5+"""""""(省略号)1+2+3+""""""'+n=?
1+2+3+省略号+99+100+99+98+省略号+3+2+1
设数列an的首项a1=1/2,an=3-a(n-1)/2,n=2,3,4省略号.
已知A=1^2+3^2+5^2+省略号+97^2+99^2,B^2=2^2+4^2+6^2+省略号+98^2+100^2
已知A=1^2+3^2+5^2+省略号+97^2+99^2,B=2^2+4^2+6^2+省略号+98^2+100^2.求
1*2+2*3*4*3*4*5*6+4*5*6*7*8+省略号+10*11*12*13*省略号*20=?
1 + 1 +2 分之1+ 1+2+3分之1 +(省略号)+1+2+3+(省略号)+100分之1
10000+9999-9998+9997省略号3-2+1=?