help with maths :-S

[klarrix]

got a big problem, and cant get hold of anybody who will know right now:
maths test tomorrow, and theres one important part i don't get, which is nth term.. (bear with me here, i know nobody likes being asked to do maths but this is life or death)

i'm ok with normal sequences that are regular

3 4 6 7 8 = tn= n + 2


but the moment it comes to the really weird ones such as

1 3 6 10 15

i get lost, and the revision guide i have says to do it with a lengthy formula that i have never used up to now... help if you have any idea how, do you think you could say, coz i dont wanna fail over this rubbish
cheers

[Lead_Head]

Ask your Maths teacher, thats what they are for, if tells you to go away and learn it yourself, then he isn't doing his job.

Either that or you haven't been listenin in lessons, so you deserve punishment

And no, sorry, I don't have a clue to your answer!

[TomWilko]

Pattern No.: 1 2 3 4 5

Sequence.: 1 3 6 10 15

Break this down into the differences between each sets of numbers, so the difference between 1 -> 3 = 2, the difference between 3 -> 6 = 3 etc etc, until u end up wif:

2 3 4 5

We can see here that the difference between the numbers is now 1. So, we now take the difference between these numbers and half it and place it in front of n^2 (n squared) so the beggining of the formula is 1/2n^2 +/- ??

We now need to find the final part of the formula (+/- ??). So what you do is find something that will match to the all the numbers. In this example, to get to the required numbers we much 1/2 our Pattern number (i.e 1, 2, 3, 4, 5) and add this to the end of the formula...this then gives a general formula to find any number in the sequence

Final formula:

1/2n^2 + 1/2n

Hope that helps and its not to confusing!! Been a while since i did one of those

...Tom

[streetster]

edit : ok beaten by someone who knows what they're talking about

[mike_w]

Firstly, you have to work out the first and second line of difference. So:

1 3 6 10 15
2 3 4 5 <---1st line of difference
1 1 1 <---2nd line of difference

Since the 2nd line of difference is constant i.e. the numbers don't change, there must be n^2 (n squared). Since 1 is 1/2 of 2 then it must be 1/2n^2. If the 2nd line of difference was 4, it would be 4/2 = 2n^2. Anyway, we now subtract 1/2n^2 away from the original sequence so:

Un=1/2n^2 + [1/2, 1, 1 1/2, 2...]

We then work out the solution to the new linear sequence and add it to the bit we just worked out (Un=1/2n^2). So:

Un=1/2n^2 + 1/2n.

Hope this helps, post again if you don't understand any (or all) of it.

Mike

[Howard]

Is the answer 1? If not, I have no idea. Lol. I'm the worst mathematician in the south of England I'm willing to bet.

[klarrix]

you're on. i got 37% in the last test.... still clinging on to set one though lol
this one's an exam tho so i'm actually bothered. i think micks got the idea i just got a couple of problems with what he put, which i can either sort out tomorrow in school or tonight on msn IF HE EVER DECIDES TO COME ON MSN WITHOUT JUST SAYING "k" THEN LEAVING...

[TomWilko]

My best advice would be to invest in a GCSE maths text book and look up 'nth' term stuff. I can not recommend this book highly enough:

http://www.amazon.co.uk/exec/obidos/...110815-8151011

Got me an 'A' for GCSE anyway

[klarrix]

hey
well that was good. after all that bloody worrying it didnt bother to show up in the test.... still got stuck on one low mark question but SURPRISE SURPRISE mick got it right...

[mike_w]

hey
well that was good. after all that bloody worrying it didnt bother to show up in the test....

Don't worry, there's still the calculator paper

[klarrix]

why do you taunt the poor kirb??