設等差數列{an}的公差爲d,若數列{}爲遞減數列,則( )(A)d>0 (B)d<0(C)a1...
問題詳情：設等差數列{an}的公差爲d,若數列{}爲遞減數列,則()(A)d>0 (B)d<0(C)a1d>0(D)a1d<0【回答】D解析:由{}爲遞減數列,知{a1an}爲遞減數列,a1an=a1[a1+(n-1)d]=a1dn+a1(a1-d),∴a1d<0.故選D.知識點：數列題型：選擇題...
問題詳情：設等差數列{an}的公差爲d,若數列{}爲遞減數列,則()(A)d>0 (B)d<0(C)a1d>0(D)a1d<0【回答】D解析:由{}爲遞減數列,知{a1an}爲遞減數列,a1an=a1[a1+(n-1)d]=a1dn+a1(a1-d),∴a1d<0.故選D.知識點：數列題型：選擇題...