一、已知Sn,求an
1.设数列{an}的前n项和为Sn， 满足S英国留学程序n=2an+1,
(1)求a1
(2)证明{an}等比，
(3)并求an
2. 设数列出国留学体检项目{an}的前n项和为Sn， 满足an=2S-2n.
(1)求a1
(2)证明{an}等比，
(3)并求an
3. 设数列{an}的前n项和为Sn， 满足Sn=an-1(1)求a1,(2)证明{an}等比，并求an
4. 设数列{an}的前n项和为Sn， 满足Sn=-2an-1,(1)求a1,(2)证明{an}等比，并求aiskn
5. 设数列{an}的前n项和为Sn， 满足an=4Sn+2,(1)求a1,(2)证明{an咀嚼的意思}等比，并求an
6南通培训网.已知数列{an}的前n项和为Sn,3Sn=an-1（1）求a1,a2；（2）求证数列{an}是等比数列。
0
二、已知Sn,求通项公式
①知Sn求an用公式
②含有的式子用
③两个转化方向：全部转化为an或全部转化为Sn
1.
2.Sn=n2+n
3. Sn=n2+2n
4.Sn=n2
5. Sn=n2+1
5. 含有双写字母的词，将双写改为单写，在词尾加t。如：keep—kept, sleep—slept, feel—felt, smell—smelt
make 制作 made made
have / has 有 had had6.Sn=n(n-1)
绞死 hanged hanged
ll 卖 sold sold
say 说 said said
win 获胜 take your time的中文意思won won
feel 触摸 felt felt
mean 表…意思 meant meant
纱灯spring 跳跃 sprang / sprung sprung
strike 敲击 struck struck
tear 撕裂 tore torn7．设数列castiel{an}的前n项和Sn=2n2，{bslippersn}西安课外辅导为等比数列，且b1=a1, b1(a2-a1)=b2.（1）求数列{an},{bn}的通项公式；
mislead 误导 misled misled
fight 作战 fought fought
read 读 read read
hide 隐藏 hid hidden / hid
dive 跳水，俯冲 dived / dove divedundo 撤消 undid undone
meet 遇到 met metforget 忘记 forgot forgot / forgotten
