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Math Help - rational equations

  1. #1
    ADY
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    rational equations

    \frac {1}{a} + \frac{1}{b} = \frac{1}{c}

    When a = \frac{4}{5} and c = \frac{2}{3}

    How can i find b?
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  2. #2
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    Quote Originally Posted by ADY View Post
    \frac {1}{a} + \frac{1}{b} = \frac{1}{c}

    When a = \frac{4}{5} and c = \frac{2}{3}

    How can i find b?
    Plug in the given values:

    \dfrac1{\frac45} + \dfrac1b=\dfrac1{\frac23}

    Move the constants to the RHS of the equation:

    \dfrac1b = \dfrac32 - \dfrac54=\dfrac14

    Thus b = 4
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  3. #3
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    Quote Originally Posted by ADY View Post
    \frac {1}{a} + \frac{1}{b} = \frac{1}{c}
    (a + b) / bc = 1 / c
    ac + bc = ab
    ab - bc = ac
    b(a - c) = ac
    b = ac / (a - c)

    Ya'll ok now ?
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  4. #4
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    Quote Originally Posted by Wilmer View Post
    (a + b) / bc = 1 / c
    ac + bc = ab
    ab - bc = ac
    b(a - c) = ac
    b = ac / (a - c)

    Ya'll ok now ?
    I don't want to pick at you but shouldn't this line

    (a + b) / bc = 1 / c

    read

    (a + b) / ab = 1 / c
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  5. #5
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    Quote Originally Posted by earboth View Post
    I don't want to pick at you but shouldn't this line
    (a + b) / bc = 1 / c
    read
    (a + b) / ab = 1 / c
    Yes, typo...thanks Mr E
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