The Student Room Group

Induction with divisibility

https://cdn.discordapp.com/attachments/322819040059850757/374672663706075156/unknown.png

I'm not quite sure why how you can stick an x behind the 11, can someone explain?
Reply 1
Original post by will'o'wisp2
https://cdn.discordapp.com/attachments/322819040059850757/374672663706075156/unknown.png

I'm not quite sure why how you can stick an x behind the 11, can someone explain?


The x means that it is a multiple of 11.
Original post by Shaanv
The x means that it is a multiple of 11.

so in otherwords it's 11 multiplied by a multiple of 11

so for example it could be that x is 121 so then 11x=1112111x=11\cdot 121 ? right
Reply 3
Original post by will'o'wisp2
so in otherwords it's 11 multiplied by a multiple of 11

so for example it could be that x is 121 so then 11x=1112111x=11\cdot 121 ? right


No its 11 multiplied by an integer. So x is just an integer.

So it could be 11*2 or 11*3 or 11*12 etc.
Original post by Shaanv
No its 11 multiplied by an integer. So x is just an integer.

So it could be 11*2 or 11*3 or 11*12 etc.


but why do i stick an integer there though?
Reply 5
Original post by will'o'wisp2
but why do i stick an integer there though?


Well this notation is unfamiliar to me however i assume that it means that 5^(2n)-3^(n) is divisible by 11 for all real values of x. So when u divide 5^(2n)-3^(n) by 11 u will always get an integer value which they have denoted with ‘x’.
Original post by will'o'wisp2
https://cdn.discordapp.com/attachments/322819040059850757/374672663706075156/unknown.png

I'm not quite sure why how you can stick an x behind the 11, can someone explain?


Huh? I struggle to find what you're pointing at to be honest...

If you mean the part where it says 52n3n=11x5^{2n}-3^n=11x then of course you're allowed to stick an x there, in fact you need to, because you are assuming here that 52n3n5^{2n}-3^n is a multiple of 11, which serves as your induction assumption that is used later on.

Here xx is just some integer, depending on your choice of nn of course in your assumption. Missing out on an xx would mean that for any nNn \in \mathbb{N} that I'd pick, I would end up with the number 11 from 52n3n5^{2n}-3^n which is counter intuitive at the very least.
(edited 6 years ago)
Original post by Shaanv
Well this notation is unfamiliar to me however i assume that it means that 5^(2n)-3^(n) is divisible by 11 for all real values of x. So when u divide 5^(2n)-3^(n) by 11 u will always get an integer value which they have denoted with ‘x’.


where is this part, i can only see n in the set of naturals in the beginning and p(n) implies there exists a z in the set of integers


anyway you always get an integer? how tho but can't you get a fraction out?
Reply 8
Original post by will'o'wisp2
where is this part, i can only see n in the set of naturals in the beginning and p(n) implies there exists a z in the set of integers


anyway you always get an integer? how tho but can't you get a fraction out?


Sorry mate im not familiar with this notation. I gave u an answer that i thought made sense based on my knowledge of induction, and i tried to extrapolate what i knew to fit what i saw.

Guess i am wrong or missing something.Sorry im not gonna be much help.
(edited 6 years ago)
Original post by RDKGames
Huh? I struggle to find what you're pointing at to be honest...

If you mean the part where it says 52n3n=11x5^{2n}-3^n=11x then of course you're allowed to stick an x there, in fact you need to, because you are assuming here that 52n3n5^{2n}-3^n is a multiple of 11, which serves as your induction assumption that is used later on.

Here xx is just some integer, depending on your choice of nn of course in your assumption. Missing out on an xx would mean that for any nNn \in \mathbb{N} that I'd pick, I would end up with the number 11 from 52n3n5^{2n}-3^n which is counter intuitive at the very least.

Oh right i see, thanks man, you're always a godsend, it's always the silly little things like these which i always miss out which makes things not make sense for me :P
Original post by Shaanv
Sorry mate im not familiar with all of this. I gave u an answer that i thought made sense based on my knowledge of induction, and i tried to extrapolate what i knew to fit what i saw.

Guess i am wrong or missing something.Sorry im not gonna be much help.


u did well i understand there has to be an integer but now i need to find out why :smile:

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