#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.

#2

-9n

#3

Divide it all by zero

#4

Thanks

#5

jimtaka has it.

Easy stuff.

Easy stuff.

#6

yeah it -9n for positive and 9n for negative numbers

#7

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.

-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.

#8

-81?

#9

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

-81?

fail

#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

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

#12

fail

that answer (-81) is actually pretty funny on a few levels

#13

Say your dog ate it

and if the teacher says its a lie say "I can show its **** if you want me to"

and if the teacher says its a lie say "I can show its **** if you want me to"

#14

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

#15

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

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?

#17

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

re-read the question, what I said was bollocks

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,*

#18

Divide it all by zero

i don't know why, but i thought that was really funny .

#19

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

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?

S1?

C2. Maybe you're on a different exam board to me lol

#21

I read it as "if n is the current term of the sequence, what is the next term"

I hate making stupid mistakes

I hate making stupid mistakes

#22

Probably. I have C1 and C2 in early June.

#23

Probably. I have C1 and C2 in early June.

Lucky you. I've got C2 on Thursday and C4 next Wednesday.

#24

I have C4 next wednesday

*hi-5*

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

*hi-5*

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

#25

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!

#26

hmm A levels...

Introductory Linear Algebra

Introductory Real Analysis

Newtonian Dynamics

Probability

fun exams times at university for me.

Introductory Linear Algebra

Introductory Real Analysis

Newtonian Dynamics

Probability

fun exams times at university for me.

#27

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

#29

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.