作者:乔山办公网日期:
返回目录:excel表格制作
1. haven’t; yet
2. the tallest boy
3. How long has
4. Has; ever been to
5. has cleaned
望采纳,感谢
growing 2. arrived (到达) 3. named(给某人起名字) 4.marks(痕迹)
5.imagine(想象)
上面答主答案有百误1. has made2. was searching3. was arguing (argue的ing形式要去度e)4. has reached (the number of加名词作主语,谓语回动词用单数)答5. Have; read
望采纳 感谢
求解过程如图,满zhidao意请采纳。
解:(I)由an2+2an=4Sn+3,可知an+12+2an+1=4Sn+1+3
两式相减得an+12-an2+2(an+1-an)=4an+1,
即2(an+1+an)=an+12-an2=(an+1+an)(an+1-an),
∵an>0,∴an+1-an=2,
∵a12+2a1=4a1+3,
∴a1=-1(舍)或a1=3,
则{an}是首项为3,公差d=2的等差内数列,
∴{an}的通项公式an=3+2(n-1)=2n+1:
(Ⅱ)容∵an=2n+1,
∴bn===(-),
∴数列{bn}的前n项和Tn=(-+…+-)=(-)=.