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Topic: Solving inequalities that involve abs value functions
Replies: 9   Last Post: Jan 5, 2005 6:30 PM

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Posts: 354
Registered: 12/6/04
Re: Solving inequalities that involve abs value functions
Posted: Jan 5, 2005 1:52 AM
  Click to see the message monospaced in plain text Plain Text   Click to reply to this topic Reply wants algebra help:
>I'm trying to solve |2x+3| <= |3x+7|
>2x+3 <= 3x+7
>2x <= 3x+4
>-x <= 4
>x >= -4
>-2x-3 <= 3x+7
>-2x <=3x+10
>-5x <= 10
>x <= -2
>WRONG! The correct solutions are x<= -4 and x>= -2 but I don't understand
>how to get these solutions algebraically.

Without checking reference to a good algebra textbook, it seems you may have
left out two more possibilities; but in any case, in your condition #2, you
forgot to switch the direction of the order relation symbol when you divided by
negative 5. You should obtain x >= -2;


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