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æåä¸é¡¹ï¼ä¹å°±æ¯ç¬¬N-1é¡¹æ¯ An=(n-1)*n/2
A1=1
A2=A1+2
A3=A2+3
â¦â¦
Aï¼n-1ï¼=A(n-2)+n
左边çåçäºå³è¾¹çå
A1+A2+A3+â¦â¦+Aï¼n-1ï¼=A1+A2+A3+â¦â¦+A(n-2)+(n-1)*n/2
å³ An=(n-1)*n/2 =n^2/2-n/2
åé¢ææ±æ¯æ°åBn=n^2/2,Cn=n/2çån项åçå
Bn=n^2/2çån项ån(n+1)(2n+1)/12
Cn=n/2çån项å:(1+n)*n/4
æ以1+3+6+10+15+â¦â¦+n=n(n+1)(2n+1)/12-(1+n)*n/4=n(n-1)(n+1)/6
æåä¸é¡¹ï¼ä¹å°±æ¯ç¬¬N-1é¡¹æ¯ An=(n-1)*n/2
A1=1
A2=A1+2
A3=A2+3
â¦â¦
Aï¼n-1ï¼=A(n-2)+n
左边çåçäºå³è¾¹çå
A1+A2+A3+â¦â¦+Aï¼n-1ï¼=A1+A2+A3+â¦â¦+A(n-2)+(n-1)*n/2
å³ An=(n-1)*n/2 =n^2/2-n/2
åé¢ææ±æ¯æ°åBn=n^2/2,Cn=n/2çån项åçå
Bn=n^2/2çån项ån(n+1)(2n+1)/12
Cn=n/2çån项å:(1+n)*n/4
æ以1+3+6+10+15+â¦â¦+n=n(n+1)(2n+1)/12-(1+n)*n/4=n(n-1)(n+1)/6
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