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Thread: Solve for x

  1. #1
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    Post Solve for x

    In school we started doing algebra but I don't know where to begin with , can someone help me please?
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    5x=15
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  2. #2
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    Re: Solve for x

    If it's a simple solve for x, it would be 15/5=3

    Some textbooks might be useful for homework help. If your school has prescribed some, just use those. Frequently getting some help from a senior might also help. Asking your teacher to explain again, should not be an issue. Most teachers are happy to help.
    Last edited by zoeyw; May 13th 2019 at 10:46 PM. Reason: Thought some additional info might be useful
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  3. #3
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    Re: Solve for x

    the key rule in algebra is anything you do to one side of the equation you must do to the other side of the equation.

    $5x = 15$

    here we would like to isolate the $x$ on one side of the equation.

    Let's multiply both sides by $\dfrac 1 5$

    $\dfrac 1 5 \cdot 5 x = \dfrac 1 5 \cdot 15$

    $x = 3$

    and voila!
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  4. #4
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    Re: Solve for x

    Quote Originally Posted by Basko View Post
    In school we started doing algebra but I don't know where to begin with , can someone help me please?
    5x=15
    5 apples cost 15 cents...
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  5. #5
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    Re: Solve for x

    Think of it as "something has been done to x and to get back to x, we have to 'undo' it". And "undoing" a mathematical operation means doing the opposite (technically the "inverse"). In 5x= 15, x has been multiplied by 5. The "opposite" of "multiply by 5" is "divide by 5" (or equivalently, as romsek said, "multiply by 1/5"). And, of course, to keep the two sides equal, whatever you do to one side of an equation you have to do to the other.
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  6. #6
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    Re: Solve for x

    A math teacher wrote down 5 * 3 = 15

    He then removed the 3 and replaced it with letter x to end up with 5 * x = 15

    He then gave that to Basko and asked him to calculate what number the x represented
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