a(n+1)=a1Ãq^n
Sn=a1ï¼1-q^nï¼/(1-q)
S2n=a1(1-q^2n)/(1-q)
Tn=[17a1(1-q^n)-a1(1-q^2n)]/(1-q)/(a1Ãq^n)
=(17-17q^n-1+q^2n)/(1-q)q^n
代å
¥q=æ ¹å·2å¾
Tn=[16-17*2^(n/2)+2^n]/(1-â2)*2^(n/2)
=-(â2+1)(16/2^(n/2)-17+2^(n/2))
æ以å½16/2^(n/2)-17+2^(n/2)åå¾æå°å¼æ¶ï¼Tnåå¾æ大å¼
令t=2^(n/2) ï¼tï¼0ï¼
æ以æ±16/t+t-17çæå°å¼
16/t+t-17â¥2æ ¹å·ï¼16/t *tï¼-17=-9
å½ä¸ä»
å½16/t=tï¼t=4ï¼å³2^(n/2)=4,n=4
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