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-   -   Interval Notation (https://www.askmehelpdesk.com/showthread.php?t=99378)

  • Jun 7, 2007, 12:36 PM
    MsTaylor23
    Interval Notation
    |5x-1|<11
    Above is the problem. This is my answer.

    5x+1<11
    5x+1-1<11-1
    5x<10

    x<10
  • Jun 7, 2007, 12:55 PM
    ebaines
    Not quite. You can always check your answer by substituting it for x back in the original equation. If you did that here you'd get:

    |5*10-1|<11, or
    49<11, which is clearly not right.

    It looks like you may have a typo in the original formula: is it |5x+1|<11, or is it |5x-1|<11?

    In general, I find it easiest to start by converting the single inequality using absolute value signs to a dual inequality without the absolute values. For example, here the first step would be:

    |5x-1| < 11
    -11 < 5x-1 <11

    Now you can use normal algebra rules to get to an expression like this: a < x < b, which tells you the range for x is from a to b. Now, can you determine what the range is for this problem?
  • Jun 7, 2007, 01:48 PM
    MsTaylor23
    It is |5x-1|<11
  • Jun 7, 2007, 01:54 PM
    ebaines
    OK, so from what I told you before can you determine the interval for x?
  • Jun 7, 2007, 01:56 PM
    MsTaylor23
    I am stomped!! I was thinking that you would add the 1 on both sides of the 11 and that leaves 5x by itself
  • Jun 7, 2007, 01:58 PM
    ebaines
    Yep - which gets you to -10<5x<12. Then divide everything by 5. That leaves x by itself, in the form a<x<b.

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