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# method of difference question (fp2) watch

1. I have come across a question with more then two terms per line and am not sure how to cancel them down? I have cancelled the like terms but am still left with way too many terms and not sure what I've done wrong

can someone point me in the right direction

paper (question 5)
https://8dedc505ac3fba908c50836f5905...%20Edexcel.pdf
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2. (Original post by Katiee224)
I have come across a question with more then two terms per line and am not sure how to cancel them down? I have cancelled the like terms but am still left with way too many terms and not sure what I've done wrong

can someone point me in the right direction

paper (question 5)
https://8dedc505ac3fba908c50836f5905...%20Edexcel.pdf
They don't quite cancel in the way that you make it out to be in your working.

+1/3 doesn't cancel out +1/3, but +1/3 and +1/3 cancels out -2/3 for example.
3. (Original post by SeanFM)
They don't quite cancel in the way that you make it out to be in your working.

+1/3 doesn't cancel out +1/3, but +1/3 and +1/3 cancels out -2/3 for example.
and +1/4 + 1/4 cancels out -1/2 and so on?
4. (Original post by Katiee224)
and +1/4 + 1/4 cancels out -1/2 and so on?
Yes.
5. (Original post by SeanFM)
Yes.
okayyy think i get it hehe thanks
6. Anyone know if cancellations like these are common in exams? Or is it usually quite simple?
7. (Original post by Student403)
Anyone know if cancellations like these are common in exams? Or is it usually quite simple?
I'm sure they'll find a way to make them difficult

But seriously, keep a cool head, write out the first few terms in a nice block, as well as the last few terms in terms of n and then see what should cancel out and you should be fine.
8. (Original post by Student403)
Anyone know if cancellations like these are common in exams? Or is it usually quite simple?
It's usually like this; it takes a little bit of observation sometimes but that's really all you need
9. (Original post by Student403)
Anyone know if cancellations like these are common in exams? Or is it usually quite simple?
Yes, they come up annoyingly. Dunno about IAL.
10. (Original post by aymanzayedmannan)
It's usually like this; it takes a little bit of observation sometimes but that's really all you need
(Original post by Kvothe the arcane)
Yes, they come up annoyingly. Dunno about IAL.
Ok thanks guys

(Original post by SeanFM)
I'm sure they'll find a way to make them difficult But seriously, keep a cool head, write out the first few terms in a nice block, as well as the last few terms in terms of n and then see what should cancel out and you should be fine.
Cheers Sean! I think they generally try to "make it difficult" (read: change it up) by having different factors outside of the summation. Haven't come across harder ones like this but Ayman/Kvothe say they do
11. What paper is this?
12. (Original post by B_9710)
What paper is this?
June 2013 (Withdrawn).
13. (Original post by Zacken)
June 2013 (Withdrawn).
Hey Zain, do you think I'd get method marks for splitting up partial fractions using algebra (adding in zeroes) instead of comparing coefficients?
14. (Original post by aymanzayedmannan)
Hey Zain, do you think I'd get method marks for splitting up partial fractions using algebra (adding in zeroes) instead of comparing coefficients?
Depends on the question wording, but you should get full marks in my opinion. I'll tag and defer to tiny hobbit here.
15. (Original post by Zacken)
June 2013 (Withdrawn).
Thank you.
16. (Original post by aymanzayedmannan)
Hey Zain, do you think I'd get method marks for splitting up partial fractions using algebra (adding in zeroes)
What do you mean? Give me an example.

Any method that works should be OK. Students from the Far East (e.g Singapore) often solve 3 by 3 simultaneous equations because they are so slick at it.
17. (Original post by tiny hobbit)
What do you mean? Give me an example.

Any method that works should be OK. Students from the Far East (e.g Singapore) often solve 3 by 3 simultaneous equations because they are so slick at it.
18. (Original post by tiny hobbit)
What do you mean? Give me an example.

Any method that works should be OK. Students from the Far East (e.g Singapore) often solve 3 by 3 simultaneous equations because they are so slick at it.
Something along these lines rather than comparing coefficients:

This is the exact amount of working I'd show on paper.

Haha, a lot of Eastern students do have interesting methods of doing problems! I've seen people doing M2/3 stuff using cool vector methods! Have you ever seen the "shoelace" formula while marking pure scripts? I use that formula to find areas in coordinate geometry problems because that's what we were taught to use the year before our IGCSEs.
19. (Original post by aymanzayedmannan)
Have you ever seen the "shoelace" formula while marking pure scripts? I use that formula to find areas in coordinate geometry problems because that's what we were taught to use the year before our IGCSEs.
This! It's massively useful, even in FP1 coordinate geometry/conic sections problems.
20. (Original post by aymanzayedmannan)
Something along these lines rather than comparing coefficients:

This is the exact amount of working I'd show on paper.

Haha, a lot of Eastern students do have interesting methods of doing problems! I've seen people doing M2/3 stuff using cool vector methods! Have you ever seen the "shoelace" formula while marking pure scripts? I use that formula to find areas in coordinate geometry problems because that's what we were taught to use the year before our IGCSEs.
This is a perfectly valid method, so it would be fine.

Yes I've come across the shoelace method, although I didn't know it was called that - a very appropriate name.

Another one is "synthetic division", a way of laying out algebraic long division.

I did once come across a number of students from one centre using vector cross products in M1.

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