设等差数列{a n }的前n项和为S n ,公差d>0,若a 2 =2,a 5 =11. (1)求数列{a n }的通项公式; (2)设 b n = S n n+a (a≠0) ,若{b n }是等差数列且 c n = 2 b 2n ,求实数a与 lim n→+∞ c 1 + c 2 +…+ c n b n +1 (b∈R) 的值.
【单选题】Lesson 14 词汇拓展--单词选择题-12 Procedural control is used in regions of the world, specifically _______ land areas and oceans, where radar coverage is either prohibitively expensive or is simply not feasibl...
【简答题】Restoring the quakehit ecosystems is a question of balancing the interests of the local people and the environment. Rural methane (沼气) projects can reduce the number of locals taking firewood from th...