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Math Help - Question Concerning a Sequence

  1. #1
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    Question Concerning a Sequence

    The sequence a1, a2, a3 ... an .... is such that an=(an-1 + an-2)/ 2 for an >= 3

    If a
    3 = 4 and a5 = 20, what is the value of a6 ?

    Please assist!! thanks in advance
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  2. #2
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    Re: Help With Maths Problem

    Have a go at finding a_4 first

    a_5 = \frac{a_4-a_3}{2}
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  3. #3
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    Re: Help With Maths Problem

    still didn't get the answer...can you solve it for me please
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  4. #4
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    Re: Help With Maths Problem

    a_5 = \frac{a_4-a_3}{2}

    20 = \frac{a_4-4}{2}

    40 = a_4-4

    40+4 = a_4

    Now you have a_4 you can find a_6 from

    a_6 = \frac{a_5-a_4}{2}

    Good luck!
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