【简答题】已知公差d不为0的等差数列{a n }中,a 1 =1,且a 1 ,a 3 ,a 7 成等比数列. (1)求通项a n 及前n项和S n ; (2)若有一新数列{b n },且b n = 1 a n a n+1 ,求数列{b n }的前n项和T n .
【简答题】在公差为 d 的等差数列{ a n }中,已知 a 1 =10,且 a 1, 2 a 2 +2,5 a 3 成等比数列. (1)求 d , a n ; (2)若 d <0,求| a 1 |+| a 2 |+…+| a n |.
【单选题】已知等比数列{a n }中,a 1 =1,且2a 2 ,3a 3 ,4a 4 成等差数列,则a 3 等于 [ ]
【判断题】集成电路手工焊接时,不得使用大于45W的电烙铁,焊接时间应不超过10S。
【简答题】S1:When security level 2 or 3 is get by the port facility you are visiting and the information was communicated to you ,what should you do on board?S2:According to the ISPS code ,I shall acknowledge t...
【简答题】苗语属于( )语系( )语族的( )语支的语言。
【单选题】You are kindly requested to supply the necessary tallymen to do ______ on board the ship during the discharging of the cargo.
D.
the work of opening and closing hatches