等比数列a1为0.5前n项和为sn.且1 024s30-(1024+1)s20+s10 =0.且an各项为正...求an
问题描述:
等比数列a1为0.5前n项和为sn.且1 024s30-(1024+1)s20+s10 =0.且an各项为正...求an
答
1024(S30-S20)-(S20-S10)=0
1024(S30-S20)=S20-S10
(S20-S10)/(S30-S20)=1024
(a11+a12+...+a20)/(a21+a22+...a30)=1024
1/(q^10)=1024
q=1/2
an=0.5^n