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<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>
<a https://www.thestudentroom.co.uk/showthread.php?t=7467335'> Year 12s: what will be the first way you research your future options? >>

IYGB question help

I have worked out the answer on part (i) but am clueless in part ii
Screen Shot 2017-05-06 at 15.39.02.png56.7KB
Reply 1
Avatar for Notnek
Notnek
21
Original post by Butterflyshy
I have worked out the answer on part (i) but am clueless in part ii

Stems:

Year 1 : 1
Year 2 : 1 + 3
Year 3 : 1 + 3 + 9
Year 4 : 1 + 3 + 9 + 27

So you're looking for the nth term of this sequence. What do you notice?
Original post by notnek
Stems:

Year 1 : 1
Year 2 : 1 + 3
Year 3 : 1 + 3 + 9
Year 4 : 1 + 3 + 9 + 27

So you're looking for the nth term of this sequence. What do you notice?


it is geometric?
Reply 3
Avatar for Notnek
Notnek
21
Original post by Butterflyshy
it is geometric?

Yes, well each term is the sum of a geometric sequence.

So Year 1 is S1S_1, year 2 is S2S_2 etc.

So the nth term of this sequence will be the same as the sum of the geometric sequence for n terms i.e. SnS_n.
Original post by Butterflyshy
it is geometric?


Yh if it was arithmetic then they wouldve had the same pattern throughout


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Original post by notnek
Yes, well each term is the sum of a geometric sequence.

So Year 1 is S1S_1, year 2 is S2S_2 etc.

So the nth term of this sequence will be the same as the sum of the geometric sequence for n terms i.e. SnS_n.


so it is 1*(1-3^n)/1-3
Reply 6
Avatar for Notnek
Notnek
21
Original post by Butterflyshy
so it is 1*(1-3^n)/1-3

Yes that's right although you can simplify it and write it in a nicer way.
which is then (1-3^n)/-2 which can be simplified to 1/2(3^n-1)
Original post by notnek
Yes that's right although you can simplify it and write it in a nicer way.


Thanks for the help I understand the question now.

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