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Math Help - Finding the next four terms of this sequence?

  1. #1
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    Finding the next four terms of this sequence?

    5n, -n, 7n...

    2a-5, 2a+2, 2a+9...

    I'm having trouble with the variables. Any problem solving help?
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  2. #2
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    Quote Originally Posted by puzzledwithpolynomials View Post
    3, 4.5, 6...
    My brain is just not working today? I don't know. I was thinking to maybe use the sequence forumla and try to derive it from there?
    Also:
    5n, -n, 7n...
    For the simplest n'th term sequence, the formula is \mathrm{n^{\mathrm{th}} \ Term} = dn+(a-d) where d is the difference between the terms, a is the first initial term and n is the term number. Thus for 3,4.5, 6, the difference between the term ( d) is +1.5, the first term ( a) is 3 thus the formula is \mathrm{n^{\mathrm{th}} \ Term} = (1.5)n + (3-1.5) = 1.5n + 1.5.

    For the second, do you mean 5n, -n, -7n? This would make the difference -6n, the first initial term 5n and thus you would be able to use the n'th term formula.
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  3. #3
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    Quote Originally Posted by puzzledwithpolynomials View Post
    5n, -n, 7n...

    2a-5, 2a+2, 2a+9...

    I'm having trouble with the variables. Any problem solving help?
    Hi puzzled,

    Are you sure about the first 3 terms of your first sequence? It would be nice if it were:

    5n, -n, -7n

    Then the common difference would be -6n. You simply add -6n four more times to get your four terms.

    In the second one, 2a-5, 2a+2, 2a+9, you have a common difference of 7. Looks like each successive term is 7 more than the previous one. So, just add 7 four more times to get the next four terms.
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