问题 填空题

如果数列{an}满足a1=3,an-an+1=5anan+1(n∈N*),则an=______.

答案

将an-an+1=5anan+1两边同除以anan+1

1
an+1
-
1
an
=5,

∴数列{

1
an
}是等差数列,
1
an
=
1
3
+
(n-1)×5=
15n-14
3

an=

3
15n-14

故答案为:

3
15n-14

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