已知数列an满足a1=a,an=an+1+2.定义数bn,bn=1/an n为正数若4﹤a﹤6,则已知数列an满足a1=a,an_数学解答

已知数列an满足a1=a,an=an+1+2.定义数bn,bn=1/an n为正数若4﹤a﹤6,则
已知数列an满足a1=a,an=an+1+2.定义数bn,bn=1/an n为正数
若4﹤a﹤6,则数列bn最大项的项数为

人气：318 ℃　时间：2019-08-17 00:38:33

解答

∵数列{an}满足a1=a,an=a(n+1)+2,
∴ a(n+1)-an=-2
∴数列{an}是首项为a1=a,公差为d=-2的等差数列,
∴an=a1+(n-1)d=-2n+2+a是递减数列,
∵4＜a＜6,-2n+2+4