Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Absolute value problem

  1. Aug 23, 2010 #1
    Suppose we have this absolute value question | x-3 | = 3 – x
    If we solve this question we break it as
    X - 3 = 3 – x or -(x - 3) = 3 - x
    Now if we solve it we come to know that the part on right is true for all real numbers
    And the part on the left is true for only 3

    I also have read that if there is a variable on right side of absolute value then we need to verify our solutions.
    Now we have two solution one is 3 and the other one is all real numbers. The first solution works but there is a problem with the second one, Suppose we have a real number 4 and we put it in our absolute value equation

    | x – 3 | = 3 – x
    | 4 – 3 | = 3 – 4
    | 1 | = -1
    Now when we verify our solution we discard the solution not satisfying the equation as in this case the second solution is not satisfying the solution. So, we have only one solution to this equation and that is 3.

    But when I saw the answer of this question in the book I saw that the answer is x < =3

    Now I am confuse please help me.
  2. jcsd
  3. Aug 24, 2010 #2


    User Avatar
    Homework Helper

    Notice that in order for the equation

    |x -3| = 3 - x

    to be satisfied, [itex] 3 - x [/itex] must be greater-than-or-equal-to zero, since the left side of the equation is. Do you see how that fact leads to the solution?
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook