求sn 1.an=3n-2 2.an=(3分之一）的n次方 3.an=2n次方-1

sn=2*3^n,求an an=n*2^n,求Sn an=2^n+n,求Sn 1.an=(2n-2)2^n求Sn 2.an=（2n+1）3^n求Sn 数列an满足a1=1/3,Sn=n(2n-1)an,求an 数列{an}前n项和为Sn,且2Sn+1=3an,求an及Sn 在{an}中an>0 Sn=1/2（an+n/an）求an a1=3,an=Sn-1+2n次方.n大于或等于2.求an和Sn a1=3,an=Sn-1+2的n次方.n大于或等于2.求an和Sn 数学等比数列练习题1.已知{An}的An=n+1/3^n求Sn2.已知{An}的An=1/n^2+3n+2求Sn 已知数列{an},a1=1,an=3an+1 1.求an Sn 2.若Sn≥56/81,求n的取值集合 已知an=(2n+1)*3^n,求Sn 1.在数列（an）中,a1=3,an+1=an+2n,求an和Sn 2.a1=3,an=(n+1) /n*an-1 看不懂看图 1.已知数列an的前n项和为Sn,且Sn=2^n,求通项an；2.已知数列an的前n项和为Sn,且Sn=n^2+3n,求通项an； 已知数列{an}满足Sn+an=2n+1.求an Sn=(（n-2）╱3)an,an=1求an急 数列an中,若Sn=-3an+2n,求an 数列an,前n项和Sn=-2an+3 求an