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29 August, 18:31

The 5th term in a sequence is 27, and each term is 3 less than the previous term. Enter an explicit rule and a recursive rule to complete the description of the sequence.

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  1. 29 August, 19:00
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    Recursive Rule = > a (n+1) = a (n) - 3

    Explicit Rule = > a (n) = 15 - (n-1) * 3

    Sequence = 39, 36, 33, 30, 27

    Explanation:

    Recursive Rule:

    Let a (n) denotes nth term and a (n-1) denotes the previous term

    We are given the each successive term is 3 less than the previous term so we can write

    a (n) = a (n-1) - 3

    we can also write

    Recursive Rule = > a (n+1) = a (n) - 3

    It still means the same. Each new term is 3 less than the previous term.

    Explicit Rule:

    We are also given that the 5th term a (5) is equal to 27 and we already know the difference between successive terms that is - 3

    a (n) = a (1) + (n-1) * d

    We need the first term to specify the explicit rule

    For the 5th term we can write

    a (5) = a (1) + (5-1) * -3

    27 = a (1) - (4) * 3

    27 = a (1) - 12

    a (1) = 27 + 12 = 39

    Explicit Rule = > a (n) = 15 - (n-1) * 3

    Verification:

    a (1) = 39

    a (2) = a (1) - (2-1) * 3 = 39 - (1) * 3 = 39 - 3 = 36

    a (3) = a (1) - (3-1) * 3 = 39 - (2) * 3 = 39 - 6 = 33

    a (4) = a (1) - (4-1) * 3 = 39 - (3) * 3 = 15 + 9 = 30

    a (5) = a (1) - (5-1) * 3 = 39 - (4) * 3 = 15 + 12 = 27

    sequence = 39, 36, 33, 30, 27

    a (n) = a (n-1) - 3

    a (5) = a (5-1) - 3 = a (4) - 3 = 30 - 3 = 27

    a (4) = a (4-1) - 3 = a (3) - 3 = 33 - 3 = 30

    a (3) = a (3-1) - 3 = a (2) - 3 = 36 - 3 = 33

    a (2) = a (2-1) - 3 = a (1) - 3 = 39 - 3 = 36

    a (1) = 39

    sequence = 39, 36, 33, 30, 27

    Conclusion:

    Hence as you can see both of the rules Recursive and Explicit have being tested and verified. The obtained results are correct.
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