【单选题】Here is a survey about how the 1,000 students from No. 2 Middle School go to school on weekdays. One third of the students going to school by bike are girls. Then according to the form below, ______ ...
【简答题】设等比数列{a n }的前n项和为S n ,已知a n + 1 = 2S n + 2 (n∈N * ). (1)求数列{a n }的通项公式; (2)在a n 与a n + 1 之间插入n个数,使这n + 2个数组成一个公差为d n 的等差数列. ①在数列{d n }中是否存在三项d m ,d k ,d p (其中m,k,p成等差数列)成等比数列?若存在,求出这样的三项,若不存在,说明理由; ②求...
【简答题】设等比数列{a n }的前n项和为S n .已知a n+1 =2S n +2( ) (1)求数列{a n }的通项公式; (2)在a n 与a n+1 之间插入n个数,使这n+2个数组成一个公差为d n 的等差数列, ①在数列{d n }中是否存在三项d m ,d k ,d p (其中m,k,p成等差数列)成等比数列?若存在,求出这样的三项,若不存在,说明理由; ②求证: .