数学练习已知等差数列{an}首项a1=3公差d=-5,依次取出项数被4除余3的项,组成数列{bn}(1)求b1和b2(2)求{bn}的通项公式

Question

数学练习
已知等差数列{an}首项a1=3 公差d=-5,依次取出项数被4除余3的项,组成数列{bn}
(1)求b1和b2
(2)求{bn}的通项公式

Answer 1

已知等差数列{an}首项a1=3 公差d=-5,an = 3 - 5(n-1) = 8 - 5n依次取出项数被4除余3的项,组成数列{bn}bn = a(4n-1) = 8 - 5(4n-1) = 13 - 20nb1 = a3 = 8 - 5*3 = -7 [b1 = 13 - 20*1 = -7]b2 = a7 = 8 - 5*7 = - 27...