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# Edexcel FP1 Proof by Induction Divisibility Acceptable Notation watch

1. When given a proof by induction question that involves a term of the form a^n and is a divisibility problem are you allowed to consider f(k+1) - a f(k) so as to remove the a^n term and make manipulation easier?

The reason I ask is because this is what I did when working through the edexcel IAL FP1 Jan 2014 paper and that method is not accounted for in the mark scheme, even under alternative methods.

Thanks in advance! Would like to be able to use on the exam if a question of this type comes up - removes a lot of the awkward stuff.

Edit: Tagged in you two as I wasn't sure if you might know?
2. (Original post by Iridann)
When given a proof by induction question that involves a term of the form a^n and is a divisibility problem are you allowed to consider f(k+1) - a f(k) so as to remove the a^n term and make manipulation easier?

The reason I ask is because this is what I did when working through the edexcel IAL FP1 Jan 2014 paper and that method is not accounted for in the mark scheme, even under alternative methods.

Thanks in advance! Would like to be able to use on the exam if a question of this type comes up - removes a lot of the awkward stuff.

Edit: Tagged in you two as I wasn't sure if you might know?
What's the exact question?
3. January 2014 FP1 IAL Question 10 part ii. https://googledrive.com/host/0B1ZiqB...%20Edexcel.pdf
4. (Original post by Iridann)
January 2014 FP1 IAL Question 10 part ii. https://googledrive.com/host/0B1ZiqB...%20Edexcel.pdf
Looks like one where you use the difference between them <I'd have thought.

In fact, that is exactly what they have done. I'm not sure what your question is?
https://7cba9babeb0db0ff9468853e0b2d...%20Edexcel.pdf

http://imgur.com/UEyzwo9
5. I prefer doing the proof for f(k+1) this way but it doesn't seem accepted.
6. (Original post by Iridann)
I prefer doing the proof for f(k+1) this way but it doesn't seem accepted.
It's correct, though. You would get all 6 marks.
7. (Original post by Kolasinac138)
It's correct, though. You would get all 6 marks.
Alright, cheers!
8. I'd double check this with teachers if I were you. Sometimes with exams it's not the correct method they want, it's the method in their syllabus to prove you've learned it correctly. I'm 90% sure you'd get the marks, though, but better safe than sorry.
9. (Original post by Rifleboy123)
I'd double check this with teachers if I were you. Sometimes with exams it's not the correct method they want, it's the method in their syllabus to prove you've learned it correctly. I'm 90% sure you'd get the marks, though, but better safe than sorry.
Yeah thanks, I think they accept it now - Just did my last past paper before the exam and they accepted the method in the mark scheme, although I did manage to do it the traditional way.

I would assume that it would just be best to use the standard one they use though. Ah well.

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