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Homework Help: Algebra problem

  1. Jun 3, 2007 #1
    Hi I'm on this question where I have to find x:

    3x+5 - 2x-1 = 3
    4 6

    and i ended up with 9x + 15 - 4x - 2 = 36
    12 = 12

    so i removed the 12s to leave me with 9x + 15 - 4x - 2 = 36

    Now for my question:

    When I am simplifying the left hand side; does it become 5x + 13 or 5x + 17 because if the equation should be written as (9x + 15) - (4x - 2) it would mean a -- which is a plus to make 5x + 17...


    edit: for some reason the denominators havent come up where i wanted them to be. but its 3x + 5 all over 4 and 2x - 1 all over 6
    and the second error is that both sides should have 12 as their denominators
     
  2. jcsd
  3. Jun 3, 2007 #2
    I'm not really sure how the problem is supposed to read. is 4 the denominator of 3x+5 and 6 the denominator of -2x-1?
     
  4. Jun 3, 2007 #3

    hage567

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    I'm confused. Is this the original equation?

    [tex]\frac{3x+5}{4} - \frac{2x-1}{6} = 3[/tex]
     
  5. Jun 3, 2007 #4
    [tex] \frac {3x+5} {4} - \frac {2x-1} {6}=3 [/tex]
     
    Last edited: Jun 3, 2007
  6. Jun 3, 2007 #5
    You beat me to it :(
     
  7. Jun 3, 2007 #6
    Error with LaTeX.

    So wait you have [tex] \frac {3x+5} {4} [/tex] and that is all divided by 12?
     
    Last edited: Jun 3, 2007
  8. Jun 3, 2007 #7
    yes the 2 equations you said are correct, thanks for sorting my one out
     
  9. Jun 3, 2007 #8
    So then everything is divided by 12?
     
  10. Jun 3, 2007 #9
    I think there is an error in your work. If both sides have a denominator of 12 are you referring to the left side and right side of the "=" sign. If so you would have [tex] \frac {3} {12} [/tex] not 36.
     
  11. Jun 3, 2007 #10
    the original equation eventually became
    9x + 15 - 4x - 2 (all divided by 12) = 36 (all divided by 12) when i simplified it.
    This is because I multiplied the denominators to make them all become 12

    then i would be able to multiple either side by 12 to leave the equation:

    9x + 15 - 4x - 2 = 36

    But the problem is whether that becomes 5x + 13 or 5x + 17 is what im wondering.
     
  12. Jun 3, 2007 #11
    i think my message has become a bit too confusing lol. basically the question are the ones that you 2 said. The denominator of 12 bit only comes up after some steps. and if i want to make them all have equal denominators, in this case 12, it would mean i would write 3 as 36/12
     
  13. Jun 3, 2007 #12
    Im totally confused to what is going on right now.
     
    Last edited: Jun 3, 2007
  14. Jun 3, 2007 #13

    hage567

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    david18, where did the 12 come from? What were you trying to do, cross multiply? I honestly can't see how you got from your first equation to the second.
     
  15. Jun 3, 2007 #14
    actually ive got it... it becomes 5x + 17 = 36 because i used the method that most people use... which is a lot better than my 'make everything have a denominator of 12' method...

    instead if you just make the left hand side have a denominator of 12 and leave the right hand side as 3...

    ... means the left hand side becomes:

    3(3x+5) - 2(2x-1) = 3
    ______________
    ........12

    (ignore dots)
    which means its -2 x -1 which is +2. Yeah the method i used was bad so I'll avoid it makes myself confused.

    does it make sense to everyone now?
     
  16. Jun 3, 2007 #15
    That's what I'm wondering also. :grumpy:
     
  17. Jun 3, 2007 #16
    This is the correct question. The Lowest common denominator is 12.
     
  18. Jun 3, 2007 #17
    Ok. Then you would have [tex] \frac {9x+15} {12} - \frac {4x-2} {12} = 3 [/tex]

    Therefore

    [tex] \frac {5x +17} {12} = 3 [/tex]
     
  19. Jun 3, 2007 #18

    hage567

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    OK, I see what you were doing.
     
  20. Jun 3, 2007 #19
    This is right, correct?
     
  21. Jun 3, 2007 #20

    hage567

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    Yes, I come up with the same answer. Sorry.
     
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