【单选题】若 -1, +1, 2 +3依次成等差数列,则 的值等于
【单选题】At present obtaining more land is only possible as _____ result of urbanization, when more farmers leave _____ rural areas to work in the city.
【单选题】若x,2x+2,x+3依次成等差数列,则x=
【判断题】使用热压灭菌器灭菌时所用的蒸汽是流通蒸汽。( )
【单选题】2016 年 9 月 15 日在酒泉发射成功的天宫二号是中国( )
【简答题】已知等差数列 { a n n } 满足a 1 =1,a 3 =6,若对任意的n∈N * ,数列{b n }满足b n ,2a n+1 ,b n+1 依次成等比数列,且b 1 =4. (1)求a n ,b n (2)设S n =(-1)b 1 +(-1) 2 b 2 +…+(-1) n b n ,n∈N*,证明:对任意的n∈N*, | S n |> 1 2 b n .
【单选题】The police got to an old school _______the farmers used as a store.
【判断题】使用热压灭菌器灭菌时所用的蒸汽是流通蒸汽。
【简答题】对负实数a,数4a+3,7a+7,a 2 +8a+3依次成等差数列 (1)求a的值; (2)若数列{a n }满足a n+1 =a n+1 -2a n (n∈N + ),a 1 =m,求a n 的通项公式; (3)在(2)的条件下,若对任意n∈N + ,不等式a 2n+1 <a 2n-1 恒成立,求m的取值范围.
【单选题】在直角坐标系中,O是坐标原点,P 1 (x 1 ,y 1 ),P 2 (x 2 ,y 2 )是第一象限的两个点,若1,x 1 ,x 2 ,4依次成等差数列,而1,y 1 ,y 2 ,8依次成等比数列,则△OP 1 P 2 的面积是 [ ]