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Math Help - subject of formula

  1. #1
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    subject of formula

    1/A = 1/A1 + 1/A2

    What does A equal to?
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  2. #2
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    Quote Originally Posted by the undertaker View Post
    1/A = 1/A1 + 1/A2

    What does A equal to?
    Here's a start:

    The common denominator for the right hand side is A_1 A_2:

    \frac{1}{A} = \frac{A_2}{A_1 A_2} + \frac{A_1}{A_1 A_2} = \frac{A_2 + A_1}{A_1 A_2}.
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  3. #3
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    Quote Originally Posted by the undertaker View Post
    1/A = 1/A1 + 1/A2

    What does A equal to?
    If you really mean \frac{1}{A}= \frac{1}{A_1}+ \frac{1}{A_2}, where A, A_1, and A_2 refer to different numbers, then go ahead and add the fractions on the right: \frac{1}{A}= \frac{A_1+ A_2}{A_1A_1}.

    Now "invert" both fractions:
    A= \frac{A_1A_2}{A_1+ A_2}
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