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# maths year 9 (grade 8)

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1. how do you use algebra to describe a sequence ?
2. (Original post by shreya kc)
how do you use algebra to describe a sequence ?
If you mean what I think you mean, you mean the nth term of a sequence so you use algebra to describe the change. (that explanation was terrible sorry)
eg if the sequence was 2,4,6,8
The nth term would be 2n
but if the sequence was 3,5,7,9
The nth term would be 2n + 1
Sort of basic examples but hopefully you get the idea
3. (Original post by Lemur14)
If you mean what I think you mean, you mean the nth term of a sequence so you use algebra to describe the change. (that explanation was terrible sorry)
eg if the sequence was 2,4,6,8
The nth term would be 2n
but if the sequence was 3,5,7,9
The nth term would be 2n + 1
Sort of basic examples but hopefully you get the idea
thank you so much!!!!!!!!!!!!!!!!!!!!!!!
4. (Original post by shreya kc)
thank you so much!!!!!!!!!!!!!!!!!!!!!!!
np
5. I think you mean the position to term rule (the nth term), this is the relationship between the position number (how many numbers into the sequence the term is) and the actual term. The term to term rule is the relationship between the terms in the sequence, so in a sequence such as 2,4,6,8, the term to term rule would be 2, this is because the numbers always go up in two. In this example, the number 2 is at position 1, the number 4 is at position 2 etc. To find the nth term, you have to find how you would get from the position number to the actual term. So, the nth term of this sequence would be 2n (times the position number by 2) the nth term will always be in the form an+b, a is always the term to term rule and b is the constant used to make the algebra work. So here, a would equal 2 as the term to term rule is 2.
Another example may be in the sequence 6,9,12 etc. The term to term rule is 3 as it always goes up in three, meaning the nth term must start with 3n. We then have to find out the constant to make it work. The number 6 is at position one, and one times 3 (3n) does not equal 3, so you have to add 3. The nth term of this sequence would therefore be 3n+3.
6. (Original post by shreya kc)
how do you use algebra to describe a sequence ?
The nth term is used to describe a sequence
6,9,12,15
Every time +3 so it's 3n
6-3 = 3 so answer = 3n+3

4,18,12,16
Every time +4 so it's 4n
4-4=0 so it's = 4n you don't need the +0

What would you do if you have to find the 127th term of the sequence 3n+3?
3x127+3 = 384

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