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Ok soon to be algebra teacher i can feel it! last one i think

  1. Apr 11, 2005 #1
    2(x-5)-(3x+3)<x-7
    2x-10--3x-3<x-7
    -1x-13<x-7
    0<6


    i can't find the rules for when the sign changes my son is convinced that if you only divide then the sign changes to > i don't remember and he of course has his book in school :mad:
     
  2. jcsd
  3. Apr 11, 2005 #2

    Hurkyl

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    I don't see where division has entered the picture. :tongue2:

    (The last step is wrong)

    Multiplying or dividing by a negative number flips the sign of an inequality.
     
  4. Apr 11, 2005 #3
    division part

    i was refering to the < sign i remember them having to change for a reason, he says only if your dividing, i thought maybe it was for sign change but i think you answered me :0 let me look at last line again
     
  5. Apr 11, 2005 #4
    2(x-5)-(3x+3)<x-7
    2x-10-3x-3<x-7
    -1x-13<x-7
    -13+7<2x
    -6<2x
    -3<x
    x>-3
     
  6. Apr 11, 2005 #5
    hmm again

    2(x-5)-(3x+3)<x-7
    2x-10--3x-3<x-7
    -1x-13<x-7 so -1x-1x is 2x<6 and that is x<3?

    whoray! did i get it!! looks like it works!
     
  7. Apr 11, 2005 #6

    Hurkyl

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    You sure -1x - 1x = 2x?
     
  8. Apr 11, 2005 #7
    Some little advice, I noticed you seem to do many steps in one line, slow it down and write it out more. It may take up more paper, but it actually saves paper because you will likely find the answer with less trys.

    Also, in these single variable problems, try to get the equation so that one side is only variables and the other side numbers.
     
  9. Apr 11, 2005 #8
    hmm i was close, thanks all my brain is fried im done for the night. i thank you all and my son will enjoy life without the phone tomorrow for starting this at 10pm :) im glad you all were kind enuf to help thank you for your time!

    thomas
     
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