1·正项等差数列是什么意思?

已知正项等差数列{an}中,a1=1,且a3,a7+2,3a9成等差数列.求数列{an}的通项公式. 已知等差数列{an}和正项等比数列{bn},a1=b1=1,a3+a7=10,b3=a4 已知正项数列an的前n项和为Sn,a1=1,（an-2）²=8Sn-1.证明an是等差数列. 已知等差数列｛an｝和正项等比数列｛bn｝,a1=b1=1,a3+a5+a7=9,a7是b3、b7的等比中项... 两个正项数列{An}{Bn}中,已知An,Bn²,An+1成等差数列,Bn²,An+1,Bn+1&# 正项数列an中,a1=1,an+1-√an+1=an+√an.证明数列an为等差数列并求通项an 已知正项数列｛an｝｛bn｝满足,对任意正整数n,都有an,bn,an+1成等差数列,bn,an+1,bn+1成等比数列 两个正项数列{an}{bn},an,bn^2,a(n+1)是等差数列,bn^2,a(n+1),b(n+1)^2是等比数列 已知正项数列{an},{bn}满足:对任意正整数n,都有an,bn,a(n+1)成等差数列,bn,a(n+1),b（n＋ 已知正项等比数列{an}中,a1=8,bn=log2an,（n属于N*）(1)求证数列{bn}是等差数列 ⒈正项等比数列{an}的公比q≠1,且a3,a5,a6成等差数列.则（a3+a5)/(a4+a6)=? 正项等差数列an,a5=8,a4*a6=60,求an和sn,设数列bn满足bn=1/sn,求Tn