1x(1+2)/2+(1+2)X(1+2+3)/3+(1+2+3)X(1+2+3+4)/4+.+(1+2+3+.+99)X(1+2++3+...99+100)/100
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1x(1+2)/2+(1+2)X(1+2+3)/3+(1+2+3)X(1+2+3+4)/4+.+(1+2+3+.+99)X(1+2++3+...99+100)/100
1x(1+2)/2+(1+2)X(1+2+3)/3+(1+2+3)X(1+2+3+4)/4+.+(1+2+3+.+99)X(1+2++3+...99+100)/100
1x(1+2)/2+(1+2)X(1+2+3)/3+(1+2+3)X(1+2+3+4)/4+.+(1+2+3+.+99)X(1+2++3+...99+100)/100
an的通项公式是
an=[n(n+1)/2*(n+1)(n+2)/2]/(n+1)=1/4n(n+1)(n+2)=1/4(n^3+3n^2+2n)
Sn=1/4[1/4n^2(n+1)^2+3*1/6n*(n+1)(2n+1)+2*n*(n+1)/2]
=1/4[1/4n^2(n+1)^2+1/2n*(n+1)(2n+1)+n*(n+1)]
不化简了
原式=S99=1/4[1/4*99^2*100^2+1/2*99*100*199+99*100]=6374362.5
第n项是(1+2+.....+n)*(1+2+......+(n+1))/(n+1)=(1+n)*n/2*(1+n+1)*(n+1)/2/(n+1)
找规律
解九宫格题目(X为未知数)9 X 2 X 7 X 8 X XX X 4 X X 9 X 6 X1 3 X 5 X X X X 24 X X 8 5 X X 1 XX 8 9 4 X 1 6 7 XX 1 X X 3 6 X X 88 X X X X 2 X 3 6X 5 X 6 X X 9 X XX X 7 X 4 X 2 X 1
请问这道题咋做 :(x)X (x+1) X (x+2) X (x+3) =360
*-----------------------------------------------*| 6 4 X | 8 X X | X X 5 || X X X | X X X | X 7 8 || X X X | X X X | X X X ||---------------+---------------+--------------- || X X X | X X X | 5 1 X || X X X | X 6 X | X X X || 8 X X | 3 5 X | 2 X X ||
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七年级下册政治复习提纲(山东人民出版社)第五单元是 青春的脚步 青春的气息别弄错了啊!格式:X X X X X X X X X 1、X X X X X X X X X X.2、X X X X X X X X X.3、X X X X X X X X X X X.
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