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Saint Petersburg Mathematical Olympiad
2009 Saint Petersburg Mathematical Olympiad
6
Periodic sequence
Periodic sequence
Source: St Petersburg Olympiad 2009, Grade 10, P6
August 30, 2017
algebra
Problem Statement
(
x
n
)
(x_n)
(
x
n
)
is sequence, such that
x
n
+
2
=
∣
x
n
+
1
∣
−
x
n
x_{n+2}=|x_{n+1}|-x_n
x
n
+
2
=
∣
x
n
+
1
∣
−
x
n
. Prove, that it is periodic.
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