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Math Help - what is..... the value?

  1. #1
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    Smile what is..... the value?

    okay the question is as follows:
    write the first three terms of tn= 5(2)^ n-1. what is the value of
    tn/tn-3?

    okay so the first three terms are as follows:
    t1= 5(2)^1-1=5X1=5
    t2= 5(2)^2-1=5X 2=10
    t3= 5(2)^3-1=5X4= 20


    okay I am a little bit confused about the next part: what is the value of
    tn/tn-3? how would I do this? thanks for your help!
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  2. #2
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    Ok, from your information t_n=5 \times 2^{n-1}. To get t_{n-3} just substitute n-3 for n. Thus t_{n-3}=5 \times 2^{(n-3)-1}=5 \times 2^{n-4}.

    Now divide the two. Can you see the simplification?
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  3. #3
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by bobbluecow View Post
    okay the question is as follows:
    write the first three terms of tn= 5(2)^ n-1. what is the value of
    tn/tn-3?

    okay so the first three terms are as follows:
    t1= 5(2)^1-1=5X1=5
    t2= 5(2)^2-1=5X 2=10
    t3= 5(2)^3-1=5X4= 20


    okay I am a little bit confused about the next part: what is the value of
    tn/tn-3? how would I do this? thanks for your help!
    t_n = 5 \left ( 2^{n-1} \right )

    So
    t_{n-3} = 5 \left ( 2^{n-4} \right )

    Thus
    \frac{t_n}{t_{n-3}} = \frac{5 \left ( 2^{n-1} \right )}{5 \left ( 2^{n-4} \right )} = \frac{2^{n-1}}{2^{n-4}} = 2^{(n-1)-(n-4)} = 2^{-1+4} = 2^3 = 8

    -Dan
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  4. #4
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    Sigh. My help again is useless.
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  5. #5
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Jameson View Post
    Sigh. My help again is useless.
    Not useless. In fact it was MY help that was useless since you posted first.

    -Dan
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