已知函数f(x)=ax+lnx,其中a为常数,e为自然对数的底数.(1)求f(x)的单调区间;(2)若a<0,且f(

2025-04-24 10:35:24
推荐回答(1个)
回答1:

(1)证明:因为an=2an-1+1(n≥2),所以an+1=2(an-1+1)(n≥2),
所以数列{an+1}是以a1+1=2为首项,以2为公比的等比数列.
(2)解:由(1)知,an+1=2?2n-1=2n,∴an=2n-1
∴bn=log2(an+1)=n;
(3)解:

1
bnbn+2
1
n(n+2)
=
1
2
1
n
-
1
n+2

∴Sn=
1
2
[(1-
1
3
)+(
1
2
-
1
4
)+…+(
1
n
-
1
n+2
)]=
1
2
(1+
1
2
-
1
n+1
-
1
n+2
)=
3
4
-
1
2(n+1)
-
1
2(n+2)