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Math Help - Equations - both addition and multiplication

  1. #1
    Junior Member Euclid Alexandria's Avatar
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    Question Equations - both addition and multiplication

    45 = -10 - y

    Here is how I tried to solve the problem. Judging from the section of the book I'm working in, there should have been some multiplication involved.

    45 + 10 = -10 - y + 10 (Add 10 to both sides.)
    55 = y

    By checking the original equation, I came up with a false statement.

    45 = -10 - 55
    45 = -65

    Any hints?
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  2. #2
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    Quote Originally Posted by Euclid Alexandria
    45 = -10 - y

    Here is how I tried to solve the problem. Judging from the section of the book I'm working in, there should have been some multiplication involved.

    45 + 10 = -10 - y + 10 (Add 10 to both sides.)
    55 = y

    By checking the original equation, I came up with a false statement.

    45 = -10 - 55

    45 = -65

    Any hints?
    After you add 10 to both sides you have,
    55=-y
    Not 55=y.
    Now multiply by negative one to get,
    -55=y
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  3. #3
    Junior Member Euclid Alexandria's Avatar
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    Smile

    Thanks for pointing out my mistake. Will multiplying by the variable on the other side work in every case? My book's example problem solves by dividing each side by -1.
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  4. #4
    Forum Admin topsquark's Avatar
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    Quote Originally Posted by Euclid Alexandria
    Thanks for pointing out my mistake. Will multiplying by the variable on the other side work in every case? My book's example problem solves by dividing each side by -1.
    Multiplying both sides of an equation by -1 gives the same result as dividing both sides by -1. It just depends on your philosophical methodology.

    -Dan
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  5. #5
    Junior Member Euclid Alexandria's Avatar
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    Thanks!
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