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Math Help - Need help yet again, direct proportionality

  1. #1
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    Need help yet again, direct proportionality

    Hi, this time its:
    Q is directly proportional to the square of R

    Q = 3 when R= 4

    a)Find a formula for Q in terms of R

    b)Work out the value of Q when R= 8


    I know you have to find K or something but please help
    Thanks
    Matt
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  2. #2
    Eater of Worlds
    galactus's Avatar
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    Thanks
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    First, find k, your constant of proportionality.

    Q=kR^{2}

    Use the initial conditions they gave you to find k.

    3=k(4)^{2}=16k

    k=\frac{3}{16}

    Q=\frac{3}{16}(8)^{2}
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