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Reply 240
Original post by Farzyy
For geometric series, how do you know when to use a(r^n-1) / r-1 or a(1-r^n) / 1-r ??

Is there a rule for using a certain one?


Doesn't matter which one you use as they both give the same answer.
Reply 241
Original post by Farzyy
For geometric series, how do you know when to use a(r^n-1) / r-1 or a(1-r^n) / 1-r ??

Is there a rule for using a certain one?


When r>1r > 1, we use Sn=a(rn1)r1{S}_{n} = \frac {a({ r }^{ n } - 1)}{r - 1}.

When r<1r < 1, we use Sn=a(1rn)1r{S}_{n} = \frac{a(1 - { r }^{ n })}{1 - r} .
Reply 242
I really could do with a wish right now - go back into time or delay the exam for a month
Reply 243
Original post by Farzyy
For geometric series, how do you know when to use a(r^n-1) / r-1 or a(1-r^n) / 1-r ??

Is there a rule for using a certain one?


No. Both of them will give the same answer.


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Reply 244
Things to do:

June 09 till Jan 12 papers
Go over series one last time
Find all the formulas for volume (shapes)
Learn how to use Cast with boundaries which are less then 0
Sleep at like 10

^ After that I'm pretty much set. Been getting around 70+ in the papers I've done so far, so should hopefully get above 80 2moro
Reply 245
Original post by Putch1
Are you sure that we don't need to prove the sine and cosine rules? Why is it in the textbook then? :frown:


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It might come up, so learn it. That's along side the proof of chapter 1 too, the factor theorem.
Reply 246
why was the Jan 11 paper so easy ?? there must be some logical reason
Reply 247
For geometric series and finding the sum. Is it always r^n or r^n-1 inside of the bracket?

I swear that on some questions the mark scheme has to the power of n, whereas others have to the power of n-1 and I can't see anything in the questions that would lead you to a certain conclusion?

Either that or I am going crazy but if anyone could clear up my doubts, would be much appreciated :smile:
Reply 248
Original post by Scorcher
For geometric series and finding the sum. Is it always r^n or r^n-1 inside of the bracket?

I swear that on some questions the mark scheme has to the power of n, whereas others have to the power of n-1 and I can't see anything in the questions that would lead you to a certain conclusion?

Either that or I am going crazy but if anyone could clear up my doubts, would be much appreciated :smile:



When you're finding a term e.g you want to find the sixth term in a series then it would be ar^(n-1), so n would be 6

When you're finding the sum it should always be r^n
(edited 11 years ago)
Reply 249
Original post by Scorcher
For geometric series and finding the sum. Is it always r^n or r^n-1 inside of the bracket?

I swear that on some questions the mark scheme has to the power of n, whereas others have to the power of n-1 and I can't see anything in the questions that would lead you to a certain conclusion?

Either that or I am going crazy but if anyone could clear up my doubts, would be much appreciated :smile:


They give you these forumlas in the formula book so if you refer to the formula book then there should be no trouble.
Reply 250
Farzy it depends on the whether r is <1 or -1. Does anyone know the rough grade boundaries for set A practise paper 4?
Reply 251
Original post by Licinius
Farzy it depends on the whether r is <1 or -1. Does anyone know the rough grade boundaries for set A practise paper 4?


Best to go for the default one of 80% = 60.

What did you get in other practise papers, im about to start them now
Reply 252
Could someone please show me how to do definite integrals on a Casio graphical calculator? :smile:


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Reply 253
God, I haven't done a sinlge past paper or mock. Will I still be able to get an A with the stock questions provided in the book?

Damnit, I'm so lazy.

anyways, you should check out maths247 on youtube, he's just amazing! I've learnt the whole C2 book with his videos, in a matter of days - thats how awesome he is at teaching maths.

But thats just me. I'm crap at Maths, tbh I'm crap at everthing except DIY stuff.
Reply 254
Oh nevermind - I actually just figured it out. :P Love how we can just check 90% of the questions on a calculator


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Original post by Tanmayee
Oh nevermind - I actually just figured it out. :P Love how we can just check 90% of the questions on a calculator


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Yeah, this helps me so much! Whenever I type it in manually I almost ALWAYS make a mistake.
Reply 256
Original post by yayifications
Yeah, this helps me so much! Whenever I type it in manually I almost ALWAYS make a mistake.


I know, and that way you don't waste ages checking your working because if the calculator says your answer is right then there's not much point in going through that whole question like ten times. :P


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Reply 257
I'VE JUST SOLVED MY FIRST EVER LOG QUESTION EVER :cry2:

Tears of joy. Man I hate logs.
the weather outside is not really my revision today.. its so nice and sunny and i'm stuck inside revising C2 :frown:
Original post by Liam_G
I'VE JUST SOLVED MY FIRST EVER LOG QUESTION EVER :cry2:

Tears of joy. Man I hate logs.


Hahahaa, I did that just like half an hour ago...feels so good! :P

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