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Math Help - inversely proprtional to the square

  1. #1
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    inversely proprtional to the square

    hi

    i am struggling on the following. any help much appreciated

    a is inversely proportional to the square of b. if a =3.6 x 10 -3 when b=2.5, determine the law of proportionality.

    what is the value of a when b =1.8

    what is the value of b when a = 4 x 10-3

    thanks
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  2. #2
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    Quote Originally Posted by paulhr1976 View Post
    hi

    i am struggling on the following. any help much appreciated

    a is inversely proportional to the square of b. if a =3.6 x 10 -3 when b=2.5, determine the law of proportionality.

    what is the value of a when b =1.8

    what is the value of b when a = 4 x 10-3

    thanks
    Hi paulrh1976,

    If a varies inversely as the square of b, then

    a=\frac{k}{b^2} where k is the constant of proportionality.

    If a=3.6 \times 10^{-3} when b=2.5, then

    3.6 \times 20^{-3}=\frac{k}{(2.5)^2}

    Solve the above equation for k.

    \boxed{k=2.25 \times 10^{-2}}

    (1) Find a when b = 1.8

    a=\frac{k}{b^2}

    Solve this: a=\frac{2.25 \times 10^{-2}}{(1.8)^2}


    (2) Find b when a=4 \times 10^{-3}

    a=\frac{k}{b^2}

    Solve this: 4 \times 10^{-3}=\frac{2.25 \times 10^{-2}}{b}
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