Recruiting more first- generation students has____ [A] reduced their dropout rates [B] narrowed the achievement gap [C] missed its original purpose [D] depressed college students 本题为单选题,请选出正确答案,谢谢!
【简答题】数列{a n }中,a 1 =2,a n+1 =a n +cn(c是常数,n=1,2,3,…),且a 1 ,a 2 ,a 3 成公比不为1的等比数列. (I)求c的值; (II)求{a n }的通项公式. (III)由数列{a n }中的第1、3、9、27、…项构成一个新的数列{b n },求 lim n→∞ b n+1 b n 的值.