# 2nd order difference equn

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Thread starter 2 years ago
#1
https://cdn.discordapp.com/attachmen...80/unknown.png

Why are both the numbers 1 and 1? I thought it'd be 2 and 1
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2 years ago
#2
enjoy math 😂😂😂😂😂 ..... i dont like math but .....i have 3math books in this semester. .....i study partial differential equations, derivatives, integration ,. so difficult 😰
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Thread starter 2 years ago
#3
(Original post by Mr.Rahul Tiwari)
enjoy math 😂😂😂😂😂 ..... i dont like math but .....i have 3math books in this semester. .....i study partial differential equations, derivatives, integration ,. so difficult 😰
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2 years ago
#4
(Original post by will'o'wisp2)
https://cdn.discordapp.com/attachmen...80/unknown.png

Why are both the numbers 1 and 1? I thought it'd be 2 and 1
Consider building a sequence adding up to n+1.

(1) You can either start with a 1, and follow up with a sequence adding up to n.

(2) Or you can start with a 2, and follow up with a sequence adding up to n-1.

How many sequences will work for (1)?
How many sequences will work for (2)?

So...?
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2 years ago
#5
may I any help you. .......you study in ... which standard .....

are you from which country
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Thread starter 2 years ago
#6
(Original post by DFranklin)
Consider building a sequence adding up to n+1.

(1) You can either start with a 1, and follow up with a sequence adding up to n.

(2) Or you can start with a 2, and follow up with a sequence adding up to n-1.

How many sequences will work for (1)?
How many sequences will work for (2)?

So...?
n sequences for 1
and n sequences for 2?
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2 years ago
#7
(Original post by will'o'wisp2)
n sequences for 1
and n sequences for 2?
No. Read carefully what I wrote and compare it with how your question defines Xn
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Thread starter 2 years ago
#8
(Original post by DFranklin)
No. Read carefully what I wrote and compare it with how your question defines Xn
Xn is the number of different sequences of which you can use 1s and 2s to make the number n

So if you start with a 1 then you can make X1 etc if you start with 2 then you make ??? it doesn't work for X1 but for every sequence after thatbut i still don't understand why it shouldn't be 2,1
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2 years ago
#9
Again, look at what I wrote, compare it to the definition of Xn, and then see if you can answer the 2 sub-questions I gave you.
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Thread starter 2 years ago
#10
(Original post by DFranklin)
Again, look at what I wrote, compare it to the definition of Xn, and then see if you can answer the 2 sub-questions I gave you.
ok, i've had a think and i think you're talking about the terms separately

so with 1 you work with any combinations of 1 and 2 and make that up to n
the number of sequences that will work when you start with 1 is n number of sequences as show by Xn where X1=1 and X2=2 etc

with 2 you can also work with any combo of 1 and 2 to make the n-1 term
the number of terms you can make when you start with 2 is n-1 because starting with 2 can't ever make X1 but it will make any other Xn provided the n is not 1
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2 years ago
#11
After all you've written, it's still not that clear what you're saying are the answers to the 2 questions I asked. I think you're saying the answers are n and n-1 in which case you are wrong (in fact it's clear you are 100% barking up the wrong tree).

In particular, stop fixating on "if you start with 2 you can't ever make X1", because this is a total red herring that is leading you astray.

I will ask the first 2 questions again, being even more explicit about what is going on:

Consider building a sequence adding up to n+1.

(1) You can either start with a 1, and follow up with a sequence of 1s and 2s which add up to n.

Now, look at the definition of X_n, and write down how many such sequences there are.

So, how many possible sequences are there in case (1)?

(2) You can either start with a 2, and follow up with a sequence of 1s and 2s which add up to n-1.

Now, look at the definition of X_n, and write down how many such sequences there are.

So, how many possible sequences are there in case (2)?

I feel you are still jumping off into your own thoughts rather than answering the questions I am asking you. You should be able to answer all 4 questions (the parts in either bold italic or italic) in considerably less than 40 characters. (And with very little effort or calculation).
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