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Math Help - Sequences

  1. #1
    Junior Member casey_k's Avatar
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    Post Sequences

    If t1 = 6, t2 = 4, t3 = 2, and tn = (tn-1 + tn-2) x tn-1, find t7.
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  2. #2
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    Quote Originally Posted by casey_k View Post
    If t1 = 6, t2 = 4, t3 = 2, and tn = (tn-1 + tn-2) x tn-1, find t7.
    Are you sure you typed the question correctly?

    According to your recursive equation you get:

    t_3 = (t_2+t_1)\cdot t_2 = (4+6)\cdot 4 = \boxed{40 \neq 2}
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  3. #3
    Junior Member casey_k's Avatar
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    Re:

    the sequence is 6, 4, 2
    the recursive formula is tn = (tn-3 + tn-2) x tn-1
    so I did it = (2+4) x 6 = 36
    and i got 2,068, 416 for t7
    but it's not right and now i'm not sure how to solve it.
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  4. #4
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    Quote Originally Posted by casey_k View Post
    If t1 = 6, t2 = 4, t3 = 2, and tn = (tn-1 + tn-2) x tn-1, find t7.
    I'm guessing here, but is this your equation?

    t_n = (t_{n-1} + t_{n-2}) \cdot t_{n-1}
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  5. #5
    Junior Member casey_k's Avatar
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    Formula

    <br /> <br />
t_n = (t_{n-3} + t_{n-2}) \cdot t_{n-1}<br />

    Sorry I didn't post my question clearly, still getting the hang of codes.
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  6. #6
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    Quote Originally Posted by casey_k View Post
    <br /> <br />
t_n = (t_{n-3} + t_{n-2}) \cdot t_{n-1}<br />

    Sorry I didn't post my question clearly, still getting the hang of codes.
    Using this equation I've got:


    n = 4:\left\{\begin{array}{lcr}t_4&=&(t_1+t_2)\cdot t_3 \\ &=&(6+4) \cdot 2 = \boxed{20}\end{array}\right.

    n = 5:\left\{\begin{array}{lcr}t_5&=&(t_2+t_3)\cdot t_4 \\ &=&(4+2) \cdot 20 = \boxed{120}\end{array}\right.

    n = 6:\left\{\begin{array}{lcr}t_6&=&(t_3+t_4)\cdot t_5 \\ &=&(2+20) \cdot 120 = \boxed{2640}\end{array}\right.

    n = 7:\left\{\begin{array}{lcr}t_7&=&(t_4+t_5)\cdot t_6 \\ &=&(20+120) \cdot 2640 = \boxed{369600}\end{array}\right.
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