问题
解答题
已知正项数列{an}满足a1=P(0<P<1),且an+1=
(1)若bn=
(2)求证:
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答案
(1)b1=
=1 a1 1 P
∴bn+1-bn=
-1 an+1
=1 an
-1+an an
=1& 1 an
故数列{bn}是以b1=
为首项,以1为等差的等差数列 1 P
(2)证明:bn=
=1 an
+(n-1)⇒an=1 p 1 n+
-11 p
∵0<p<1
⇒an= ∴
-1>01 p
<1 n+
-11 p 1 n
+a1 2
+a2 3
+…+a3 4
<an n+1
+1 2×1
+1 3×2
+…+1 4×3 1 (n+1)n
=1-
+1 2
-1 2
+1 3
-1 3
+…+1 4
-1 n 1 n+1
=1-
<11 n+1