已知二次函数f(x)=ax2+bx+c经过点(0,0),导数f′(x)=2x+1,当x∈[n,n+1](n∈N*)时,f(x)是整

2025-06-20 22:39:01
推荐回答(1个)
回答1:

(1)∵f(0)=c=0
∴c=0,
f′(x)=2ax+b=2x+1
∴a=1,b=1
(2)依题意可知an=(n+1)(n+2)-n(n+1)+1=2(n+1)+1,an+1=(n+2)(n+3)-(n+1)(n+2)+1=2(n+2)+1,
∴a(n+1)-an=2,a1=5
∴数列{an}是以5为首项,2为公差的等差数列,
∴an=5+(n-1)×2=2n+3
(3)bn=

2
anan+1
=
1
2n+3
-
1
2n+5
,{bn}的前n项和 Sn=
1
5
-
1
7
+
1
7
-
1
9
+…+
1
2n+3
--
1
2n+5
=
1
5
--
1
2n+5
=
2n
5(2n+5)