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# Maths C2- Series help, arithmetic, geometric etc...... watch

1. 1, 2, 4, 8..........

Q1) Arithmetic or Geometric?
Q2) What is the difference
Q3) What is the last term (Un)
Q4) What is the 20th term
Q5) Sum of all terms?
Q6) Sum of 10 terms!!!

I missed 4 lessons, somebody help me out, please.
2. (Original post by TWF)
I missed 4 lessons, somebody help me out, please.
3. (Original post by Glutamic Acid)
It's homework, in for today, in 45 minutes. Help.....
4. (Original post by Glutamic Acid)
Why ****** bother joinging a help forum to post trash like that?

Ok, if its not to late

A geometric sequence has a 'common ratio' an arithmetic has a common difference

SO is the sequence going up by the same number? no..therefore it may be geometric

To check, divide each term by the previous. If the number is the same you have your common ration.

Now...the rest of the questions (IIRC) need numerous formula..if you have the time, find them and use them once you have found the first term (a) and the common ratio (r)

to find a term in a geometirc sequence ar^(n-1)
sum will be (a(R^n - 1))/(R-1) and sum to infinity will be a/(1-r)

That should get you going as I forgot the whole question

That will get you going.
5. (Original post by dexter -1)
Why ****** bother joinging a help forum to post trash like that?
It's not trash, I'm directing him to a useful source. When this forum is used as a help forum, its intention is to help people who've thought about a topic or question for a bit, are stuck/curious to know more, and people will reply. But there's little use trying to teach someone an entire topic (especially when it's forced to be rushed by handing in homework); TSR isn't a direct substitute for school. Nothing you've said is wrong (though the sum to infinity only exists for |r|<1), but in most C2 courses geometric progressions and series will consume an entire chapter, and, though you were trying to be helpful, condensing it into half a dozen lines will make it lose all of the subtleties discovered when one learns it in school, or at least from reading a textbook. But more important when it's taught, or at least when read in a thorough textbook. But mainly school; for most people find being taught a more natural way of learning that just reading through notes/textbooks, and indeed that's why lecturers exist. I just think it would've been better all round if the original poster had admitted to not doing the homework and asked for help, rather than trying to hand in not-completely-understood work from a super-condensed half-a-dozen lines on an Internet forum.
6. (Original post by Glutamic Acid)
It's not trash, I'm directing him to a useful source. When this forum is used as a help forum, its intention is to help people who've thought about a topic or question for a bit, are stuck/curious to know more, and people will reply. But there's little use trying to teach someone an entire topic (especially when it's forced to be rushed by handing in homework); TSR isn't a direct substitute for school. Nothing you've said is wrong (though the sum to infinity only exists for |r|<1), but in most C2 courses geometric progressions and series will consume an entire chapter, and, though you were trying to be helpful, condensing it into half a dozen lines will make it lose all of the subtleties discovered when one learns it in school, or at least from reading a textbook. But more important when it's taught, or at least when read in a thorough textbook. But mainly school; for most people find being taught a more natural way of learning that just reading through notes/textbooks, and indeed that's why lecturers exist. I just think it would've been better all round if the original poster had admitted to not doing the homework and asked for help, rather than trying to hand in not-completely-understood work from a super-condensed half-a-dozen lines on an Internet forum.
It's not like I don't get it, I was taught it, and handed this piece for homework last Thursday. But I missed all lessons after that until today, I just used it as an excuse for not knowing. How can I be given it for homework if I haven't been taught it? Lol....

(Original post by dexter -1)
Why fcukin bother joinging a help forum to post trash like that?

Ok, if its not to late

A geometric sequence has a 'common ratio' an arithmetic has a common difference

SO is the sequence going up by the same number? no..therefore it may be geometric

To check, divide each term by the previous. If the number is the same you have your common ration.

Now...the rest of the questions (IIRC) need numerous formula..if you have the time, find them and use them once you have found the first term (a) and the common ratio (r)

to find a term in a geometirc sequence ar^(n-1)
sum will be (a(R^n - 1))/(R-1) and sum to infinity will be a/(1-r)

That should get you going as I forgot the whole question

That will get you going.
Thanks. That's all I needed, a start, it's not like I posted the whole sheet.

P.S. she gave me an extra day, luckily.
7. (Original post by Glutamic Acid)
It's not trash, I'm directing him to a useful source. When this forum is used as a help forum, its intention is to help people who've thought about a topic or question for a bit, are stuck/curious to know more, and people will reply. But there's little use trying to teach someone an entire topic (especially when it's forced to be rushed by handing in homework); TSR isn't a direct substitute for school. Nothing you've said is wrong (though the sum to infinity only exists for |r|<1), but in most C2 courses geometric progressions and series will consume an entire chapter, and, though you were trying to be helpful, condensing it into half a dozen lines will make it lose all of the subtleties discovered when one learns it in school, or at least from reading a textbook. But more important when it's taught, or at least when read in a thorough textbook. But mainly school; for most people find being taught a more natural way of learning that just reading through notes/textbooks, and indeed that's why lecturers exist. I just think it would've been better all round if the original poster had admitted to not doing the homework and asked for help, rather than trying to hand in not-completely-understood work from a super-condensed half-a-dozen lines on an Internet forum.
Utter rubbish. You are now trying to justify your actions with more garbage.
Why bother being part of a forum if you tell someone looking for help to go back to their teacher.
8. (Original post by dexter -1)
Utter rubbish. You are now trying to justify your actions with more garbage.
Why bother being part of a forum if you tell someone looking forhelp to go back to their teacher.
"Trash, rubbish, garbage", do yu think that if you exhaust every synonym for "waste" then the words you put together may constitute an argument? You've completely ignored my post, and just restated yourself, and I'm forced to conclude you're incapable of having a reasonable discussion, good day.
9. I shall go ask my teacher to help me with synonyms...that of course is what this forum is all about.
10. You first need to know the basics:

Arithmetic progressions

a1=first term
d= common difference for Arithmetic progressions
ak=general term
an or l=last term

Arithmetic progressions are such that there is common difference across the whole progression ie. a progression with d=5 and a1=3:

3,8,13,18...

The formulae you should learn for A.P.s are:

general term ak=a1+(k-1)d
last term an=a1+(n-1)d
Sum to n terms = Sn=n/2(2a+(n-1)d)

Geometric progressions

r=common ratio

A geometric progression is one which you multiply the previous term by a common ratio

general term:ak=ar^(k-1)
Sum of terms: Sn=(a(1-r^n))/(1-r))
Sum to infinity: S∞= a/(1-r) and the conditions for convergence is that -1< r <1

The example you gave is clearly geometric with a common ratio of 2

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