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Math Help - need linear equation help

  1. #1
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    need linear equation help

    F = (9/5)C +32
    If (x + 10)C = xF, find x.

    The answer is x = −62.5.
    But how to work it out?
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  2. #2
    MHF Contributor alexmahone's Avatar
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    Quote Originally Posted by Garp View Post
    F = (9/5)C +32
    If (x + 10)C = xF, find x.

    The answer is x = −62.5.
    But how to work it out?
    Since you have 3 variables and only 2 equations, you cannot solve for x. You need some additional information.
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  3. #3
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    Quote Originally Posted by alexmahone View Post
    Since you have 3 variables and only 2 equations, you cannot solve for x. You need some additional information.
    Here's the whole thing.

    The formula for converting degrees Celsius, C, to degrees Fahrenheit, F, is F = (9/5)C + 32.
    a Convert 30◦F to Celsius.
    b Convert 30◦C to Fahrenheit.
    c If x◦C = x◦F find x.
    d If (x + 10)◦C = x◦F find x.
    e If 2x◦C = x◦F find the value of x. f If k◦F = (−3k)◦C find k.
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  4. #4
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    Quote Originally Posted by Garp View Post
    F = (9/5)C +32
    If (x + 10)C = xF, find x.

    The answer is x = −62.5.
    But how to work it out?
    \frac{9}{5}(x+10)+32=x

    \frac{9}{5}(x+10)=x-32

    9(x+10)=5x-160

    solve for x
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  5. #5
    Senior Member BAdhi's Avatar
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    it's not (x+10)C=xF, but (x + 10)◦C = x◦F

    you've mixed up units and variables

    so substitute (x+10) to C in and x to F for the given formula
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  6. #6
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    Quote Originally Posted by BAdhi View Post
    it's not (x+10)C=xF, but (x + 10)◦C = x◦F

    you've mixed up units and variables

    so substitute (x+10) to C in and x to F for the given formula
    Haha, forgive my stupidity. >.<

    thanks for everyone that helped me!
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  7. #7
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    Quote Originally Posted by Garp View Post
    Haha, forgive my stupidity. >.<

    thanks for everyone that helped me!
    It's not stupidity, it's a subtle but important point.
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