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How subtract 2 equations?

  1. Jun 16, 2011 #1
    Hi,

    I would like to solve this equation but I can't do it.

    2x+1-((2x+3)/2)

    Can you help me?

    Thanks,
     
  2. jcsd
  3. Jun 16, 2011 #2

    Doc Al

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    Staff: Mentor

    First simplify the stuff in the parentheses: carry out the division.

    (Those are expressions, not equations. No equals sign!)
     
  4. Jun 16, 2011 #3
    This expression is the same as the following 2x+1-4x-6?

    I've multiplied ((2x+3)/2) by 2, and removed the parenthesis.
     
  5. Jun 16, 2011 #4

    Doc Al

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    Staff: Mentor

    No.
    If you had an equation, you could multiply both sides by 2. But here you just have an expression. Divide by 2.

    If you really mean to subtract two equations, please show those equations.
     
  6. Jun 16, 2011 #5

    HallsofIvy

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    Staff Emeritus
    Science Advisor

    No, you can't just multiply by 2 and get the same result- and you surely can't multiply just part of an expression and expect to get any thing sensible. And, by the way, multiplying (2x+3)/2 by 2 would just cancel the 2 in the denominator to give 2x+ 3, not 4x+ 6.

    You could write the first part as [itex](2/2)(2x+ 1)= (4x+2)/2[/tex] so you can add the fractions (remember getting a "common denominator" so you can add?):
    [tex]\frac{4x+2}{2}- \frac{2x+3}{2}= \frac{4x+ 2- 2x- 3}{2}= \frac{2x- 1}{2}[/tex]
     
  7. Jun 16, 2011 #6

    Mark44

    Staff: Mentor

    Fixed (?) LaTeX.
     
  8. Jun 16, 2011 #7

    Mark44

    Staff: Mentor

    As already noted, this is not an equation, it's an expression. The best you can do with an expression is to rewrite it in a different and possibly more simplified form.

    It's important to understand the difference between an equation (there's an =) and an expression, since there are many more things you can do to an equation, such as add a number to both sides, multiply both sides by a number, and so on.

    With an expression, the only thing you can add is 0 (in some form) or multiply by 1 (in some form), or expand or factor to write the expression in a different form.
     
  9. Jun 16, 2011 #8
    In addition to Mark44's suggestion, try to get them with the same denominator.
     
  10. Jun 18, 2011 #9

    Mark44

    Staff: Mentor

    This makes no sense in the context of this thread. The OP's problem is to simplify an expression. There is no equation.
     
  11. Jun 21, 2011 #10
    2x + 1 - ((2x + 3)/2)
    2x + 1 - (x + 3/2)
    2x + 1 - x - 3/2
    x - 1/2


    This is the step by step answer to your question.
     
  12. Jun 26, 2011 #11
    2x+1-((2x+3)/2)

    =(4x+2-2x-3)/2
    =(2x-1)/2


    :wink:
     
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