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# Need help on arithmetic sequences! watch

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1. I really can't seem to do this past paper question concerning sequences - any help will do ! thanx

The terms of a sequence are given by
Un = (n+k)², n >=1,
where k is a positive constant
Given that U2=2u1,
a)find the value of k and ...
b) show that U3 = 11 + 6√2
2. (Original post by cat123)
I really can't seem to do this past paper question concerning sequences - any help will do ! thanx

The terms of a sequence are given by
Un = (n+k)², n >=1,
where k is a positive constant
Given that U2=2u1,
a)find the value of k and ...
b) show that U3 = 11 + 6√2
using U2=2U1
U2=(2+k)^2=2(1+k)^2
4+4k+k²=2+4k+2k²
k²=2
k=√2
then
U3=(3+√2)^2=9+6√2+2=11+6√2

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Updated: November 19, 2005
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