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Homework Help: Just to solve for x

  1. Jan 12, 2010 #1
    1. The problem statement, all variables and given/known data

    12x^2 - 9 = 0

    2. Relevant equations

    3. The attempt at a solution

    Im having doubts about how to start

    I could factorize for 3(4x^2 - 3) = 0

    or to pass -9 to the other side 12x^2 = 9 and keep solving.

    What should I do?

  2. jcsd
  3. Jan 12, 2010 #2


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    Homework Helper

    Just keep solving.
  4. Jan 12, 2010 #3


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    Staff Emeritus
    Science Advisor
    Gold Member

    Pick one and try it.

    If you can't solve the problem, pick the other one.

    If you can't solve the problem, go back to the first one (or try finding a third option).
  5. Jan 12, 2010 #4
    well the result on my book is - and + 1/2 square root of 3

    If i keep solving I get 12x = +and- square root of 9 then x = +and- 3/ 12 then x = +and- 1/4 which is different.
  6. Jan 12, 2010 #5
    do this step by step

    first take the 9 over which gives:

    12x^2 = 9

    then what would u do?
  7. Jan 12, 2010 #6
    I would move the square to the right, and I would have 12x = square root of nine isnt it?
  8. Jan 12, 2010 #7


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    Homework Helper

    When you make an operation in solving equations, you need to perform the operation on both sides, but not only that, you need to perform squaring, square-rooting, etc. for every factor.

    e.g. If we have [tex]x^2=a^2b[/tex] then to solve for x you're obviously going to take the square root of both sides. This gives us [tex]x=\sqrt{a^2b}[/tex] (lets ignore the [itex]\pm[/itex] for the moment) and if you use the property of square roots, you'll have [tex]x=\sqrt{a^2}\sqrt{b}[/tex] and simplifying, [tex]x=a\sqrt{b}[/tex]

    Now look at your problem: You didn't follow the above for when you took the square root of [tex]12x^2[/tex].
  9. Jan 12, 2010 #8
    the ^2 only applies to the x

    so remember it's 12 * x^2 = 9
  10. Jan 12, 2010 #9
    take the 12 to the other side
  11. Jan 12, 2010 #10
    you are right x^2= 9/12 then x^2 = 3/4 and then to include the square root.
    x = square root of 3/4

    = 1/2 square root of 3 thanks a lot guys.. I appreciate it .
  12. Jan 12, 2010 #11


    Staff: Mentor

    There are two answers...
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