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# C2/FP1 sequence Watch

1. How do I find the rth term of
I can find the rth/nth term for arithmetic/geometric series but when it is sequences like these I can't find a relation.

Thanks
2. 1st term 1 x 2
2nd term 3 x 4
3rd term 5 x 6

Can you really not see any patterns in these numbers?

Look at the term number as the last number in the product?
3. Oops ignore that post.
4. (Original post by CD315)
Oops ignore that post.
That doesnt even work tho.
5. (Original post by UKBrah)
That doesnt even work tho.
So have you worked it out yet?

What is the connection between 1 and 2, 2 and 4, 3 and 6, 4 and 8 ... ?

Hence what is the connection between 1 and 1, 2 and 3, 3 and 5, 4 and 7 ...?
6. (Original post by Mr M)
So have you worked it out yet?
I can't make sense of any patterns, Mr M.

I dont know what im not understanding

Ah, so the difference between 1 and 2 is 1. Then the difference between 2 and 4 is 2. Then the difference between 3 and 6 is 3 etc.

The differences keep getting bigger? by 1 that is.
7. (Original post by UKBrah)
That doesnt even work tho.
See my post on the A-level thread..
8. (Original post by UKBrah)
I can't make sense of any patterns, Mr M.

I dont know what im not understanding
You genuinely can't see a pattern here?

1 and 2
2 and 4
3 and 6
4 and 8
5 and 10
6 and 12
7 and 14

etc
9. (Original post by Mr M)
You genuinely can't see a pattern here?

1 and 2
2 and 4
3 and 6
4 and 8
5 and 10
6 and 12
7 and 14

etc
1 and 2 +1 n(n+1)
2 and 4 +2 (n+1)(n+2)
3 and 6 +3 (n+2)(n+3)
4 and 8 +4 (n+3)(n+4)
5 and 10 +5
6 and 12 +6
7 and 14 +7

or is this meaningless
10. (Original post by UKBrah)
1 and 2 +1 n(n+1)
2 and 4 +2 (n+1)(n+2)
3 and 6 +3 (n+2)(n+3)
4 and 8 +4 (n+3)(n+4)
5 and 10 +5
6 and 12 +6
7 and 14 +7

or is this meaningless
Meaningless.

The first number is the TERM number not a product.
11. Let's try again.

Can you write an expression for the nth term of this sequence?

2, 4, 6, 8, 10, 12, 14, 16, 18 ...
12. (Original post by Mr M)
Meaningless.

The first number is the TERM number not a product.
im seriously not understanding the pattern. should I go shoot myself?
13. (Original post by Mr M)
Let's try again.

Can you write an expression for the nth term of this sequence?

2, 4, 6, 8, 10, 12, 14, 16, 18 ...
Thanks for baring with me
nth term would be 2n?
14. (Original post by UKBrah)
Thanks for baring with me
nth term would be 2n?
Yes!

Now do the same for this.

1, 3, 5, 7, 9, 11 ...

15. (Original post by UKBrah)
im seriously not understanding the pattern. should I go shoot myself?
Have a look at Mr M's sequence again, and consider what is 2x1 etc.
16. (Original post by Mr M)
Yes!

Now do the same for this.

1, 3, 5, 7, 9, 11 ...

un = 2n-1
17. (Original post by UKBrah)
un = 2n-1
Yes!

Now write down the nth term of this sequence.

1 x 2
3 x 4
5 x 6
7 x 8
9 x 10

etc
18. (Original post by Mr M)
Yes!

Now write down the nth term of this sequence.

1 x 2
3 x 4
5 x 6
7 x 8
9 x 10

etc
I was using the nth term formula for arithmetic sequences tho previously and not inspection.
19. (Original post by UKBrah)
I was using the nth term formula for arithmetic sequences tho previously and not inspection.
I have no idea what you are saying but this is how you are supposed to answer this question. Have you succeeded yet?
20. (Original post by Mr M)
I have no idea what you are saying but this is how you are supposed to answer this question. Have you succeeded yet?
I think Ive clocked onto something..
So if I consider the sequence formed by the left of the product of the terms it forms a sequence 1,3,5 etc and same for the right, 2,4,6,8 etc.
The nth term for both of those is (2n-1) and 2n respectively, so can I multiply them together to form (2n-1)2n? It works!

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Updated: March 30, 2013
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