# sequence and series

1) A sequence is defined by Un+1=Un+2Un-1
a) Given that U11=683 and U8=85 deduce the equations
U10+2U9=683
U10- U9=170

b) Find the value of U9

 ebaines Posts: 10,033, Reputation: 5529 Expert #2 Apr 3, 2012, 05:55 AM
This is a continuation of the sam question yuo asked earlier here: http://www.askmehelpdesk.com/mathema...rs-647105.html

If the sequence is

$
U_{n+1} = U_{n} + U{n-1}
$

The first question is simply applying n=10:

$
U_{(10+1)} = U_{10} + 2 U_{(10-1)}, \\
U_{11} = U_{10} + 2 U_9
$

For the second use n=9, and rearrange to get the result.

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