ï¼1ï¼f '(x)=2x+1 ï¼å æ¤ a(n+1)=2an+1 ï¼ä¸¤è¾¹å 1 å¾ a(n+1)+1=2(an+1) ï¼
å æ¤æ°åï½an+1ï½æ¯é¦é¡¹ä¸º a1+1=2 ï¼å
¬æ¯ä¸º 2 ççæ¯æ°åï¼
å æ¤ an+1=2^n ï¼æ以 an = 2^n - 1 ã
ï¼2ï¼nan=n(2^n-1)=n*2^n-n ï¼
æ以å n 项å为 Sn=(1*2^1+2*2^2+3*2^3+....+n*2^n) - 1/2*n(n+1) ï¼
èå¯ T=1*2^1+2*2^2+3*2^3+.....+n*2^n ï¼
ä¹ä»¥ 2 å¾ 2T=1*2^2+2*2^3+3*2^4+......+(n-1)*2^n+n*2^(n+1) ï¼
ç¸åå¾ T=2T-T
= -2-2^2-.....-2^n+n*2^(n+1)=2-2^(n+1)+n*2^(n+1)=2+(n-1)*2^(n+1) ï¼
æ以 Sn = 2+(n-1)*2^(n+1)-1/2*n(n+1)=(n-1)*2^(n+1) - 1/2*(n^2+n-4) ã
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