#1
Hey UG, could anyone tell me how to figure out the expression for the nth term in the sequence -9,-18,-27,-36? I've tried google searching how to figure it out but nothing really helped.
#7
Quote by GunsN'tallica
Hey UG, could anyone tell me how to figure out the expression for the nth term in the sequence -9,-18,-27,-36? I've tried google searching how to figure it out but nothing really helped.


Quote by jimtaka
-9n


Correct. You should be looking for the 'common difference' between terms, as it will help you identify a pattern.

Here, the 1st term -9 and second term -18, identify a -9n rule, because of the difference. You should usually find the common difference, as it will help you figure out basic progressions well.

2,5,8,11. Common difference is 3. So I suggest the rule is 3n. That would give me 3, 6, 9, 12. So not quite there -> So I take one off, to make the rule for an nth term; 3n-1. This gives me 2,5,8,11. I've got it.

If you don't see where I'm coming from, read up on some maths sites - progressions are pretty easy marks in exams, even up to A-Level.
#9
Quote by Mazzakazza
Correct. You should be looking for the 'common difference' between terms, as it will help you identify a pattern.

Here, the 1st term -9 and second term -18, identify a -9n rule, because of the difference. You should usually find the common difference, as it will help you figure out basic progressions well.

2,5,8,11. Common difference is 3. So I suggest the rule is 3n. That would give me 3, 6, 9, 12. So not quite there -> So I take one off, to make the rule for an nth term; 3n-1. This gives me 2,5,8,11. I've got it.

If you don't see where I'm coming from, read up on some maths sites - progressions are pretty easy marks in exams, even up to A-Level.


Thanks for clearing that up for me
#10
Quote by K!!LsWiTcH
-81?

fail
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#11
For an Arithmetic Sequence, the formula for the nth term is;

a + (n-1)d
Where a is the first term, n is n and d is the common difference.
Decide your values. a is going to be -9 and d will be -9 also.

So term number n is;

-9 + (n-1)-9

-9 -9n +9

Nines go so you get -9n, and it works. If you put in term 2 you get -18 which is the answer. So the 51st term would be -9 times 51 which is 459
I hope it doesn't seem, like I'm young, foolish, and green.
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O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre
#12
Quote by riffmasterjosh
fail

that answer (-81) is actually pretty funny on a few levels
#15
Quote by RubberPuppiessu
Say your dog ate it
and if the teacher says its a lie say "I can show its **** if you want me to"


Lol I cant. We have this assessment thingy over the internet that we have to do..
#16
Quote by chubbychunks
Arithmetic and geometric progressions are the only fun thing in A levels maths.

Boo. Trig is the best.
How can anyone say no to a^2 = b^2 + c^2 - 2bc cosA

And are you looking forward to the exam on Thursday morning?
I hope it doesn't seem, like I'm young, foolish, and green.
Let me in for a minute, you're not my life but I want you in it


O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre
#17
Wait till you get onto Core 3 and 4, now that's trig

Quote by chubbychunks
Arithmetic and geometric progressions are the only fun thing in A levels maths.



this isn't A level progression though, this is more KS3 or GCSE

re-read the question, what I said was bollocks
Last edited by Rocking-Rob at May 13, 2008,
#19
Quote by BlackLuster
Boo. Trig is the best.
How can anyone say no to a^2 = b^2 + c^2 - 2bc cosA

And are you looking forward to the exam on Thursday morning?

S1?
#20
Quote by Rocking-Rob
Wait till you get onto Core 3 and 4, now that's trig


this isn't A level progression though, this is more KS3 or GCSE

and surely its n-9 not -9n

because if it were -9n then the first term -9 would lead to the second term being 81

Are you thinking of geometric progressions?

Quote by chubbychunks
S1?

C2. Maybe you're on a different exam board to me lol
I hope it doesn't seem, like I'm young, foolish, and green.
Let me in for a minute, you're not my life but I want you in it


O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre
#23
Quote by chubbychunks
Probably. I have C1 and C2 in early June.

Lucky you. I've got C2 on Thursday and C4 next Wednesday.
I hope it doesn't seem, like I'm young, foolish, and green.
Let me in for a minute, you're not my life but I want you in it


O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre
#25
Quote by Rocking-Rob
I have C4 next wednesday

*hi-5*

C3 I think is three weeks today, and S2 (I hate stats) a month away

High Five

C3 is then as well, luckily for me on my second stab at it I scraped a B.
And how can you hate S2????? It's my favourite section of A level maths so far. Chi squared tests, Spearman Rank. Ah, those were the days.
Although all that Normal/Binomial/Poisson crap really gets on my tits.

Don't forget, e^-lamda x Lamda^r over r!
I hope it doesn't seem, like I'm young, foolish, and green.
Let me in for a minute, you're not my life but I want you in it


O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre
#26
hmm A levels...

Introductory Linear Algebra
Introductory Real Analysis
Newtonian Dynamics
Probability

fun exams times at university for me.
"And after all of this, I am amazed...

...that I am cursed far more than I am praised."
#27
Quote by BlackLuster
High Five

C3 is then as well, luckily for me on my second stab at it I scraped a B.
And how can you hate S2????? It's my favourite section of A level maths so far. Chi squared tests, Spearman Rank. Ah, those were the days.
Although all that Normal/Binomial/Poisson crap really gets on my tits.

Don't forget, e^-lamda x Lamda^r over r!



I'm just no fan of stats, its not hard per sé but I just find it dull.

I'll need to start revising seeing as I've had no stats teacher since december, yay for doing most of my maths course at home.
#28
Am I the only one who is curious as to why this thread still exists? The answer has been given, move on
Quote by mustaineNslash
i know this sounds stupid but...
wheres the sig button??

(sry)


#29
Quote by aleb
Am I the only one who is curious as to why this thread still exists? The answer has been given, move on

Report the thread if it bothers you that much.
I hope it doesn't seem, like I'm young, foolish, and green.
Let me in for a minute, you're not my life but I want you in it


O Dayya, te echaré de menos, siempre

Y siempre
Y para siempre