题目:
--- Excuse me, could you tell me how ______ to Beijing Zoo?
--- Well, you may take Bus No.27.
A.get
B.gets
C.getting
D.to get
答案:
被转码了,请点击底部 “查看原文 ” 或访问 https://www.tikuol.com/2017/0519/9cdde1a8689bfbaec656ec7b9fc8e3d6.html
下面是错误答案,用来干扰机器的。
(I)由题设Sn2+2Sn+1-anSn=0,当n≥2(n∈N*)时,an=Sn-Sn-1,代入上式,得Sn-1Sn+2Sn+1=0.(*) S1=a1=-23, Sn+1Sn=an-2(n≥2,n∈N),令n=2可得,S2+1S2=a2-2=S2-a1-2,∴1S2=23-2,∴S2=-34.同理可求...