1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Teacher told to set absolute value inequality to equal 0

  1. Mar 25, 2015 #1
    So I was helping my sister on homework and there was this problem:
    2 abs(2x + 4) +1 > or equal to -3
    teacher told her to ignore the -3 and just set it equal to zero.
    Soo should you? This question got me confused. can't you just go about solving, bringing the 1 to the left and then dividing by 2?
    EDIT: when I do it I get interval notaion from -3 to 3
    and with the zero thing i get -2.5 to 2.5
    Last edited: Mar 25, 2015
  2. jcsd
  3. Mar 25, 2015 #2


    Staff: Mentor

    ##2|2x + 4| + 1 \ge -3##
    ##\Leftrightarrow 2|2x + 4| \ge -4##
    ##\Leftrightarrow |2x + 4| \ge -2##
    Since the absolute value is always greater than or equal to zero, you can change the last inequality to ##|2x + 4| \ge 0##.
  4. Mar 25, 2015 #3


    User Avatar
    Science Advisor

    |anything|≥0. Therefore 2|2x+4|+1≥1 for all x. Any x will do.
  5. Mar 25, 2015 #4


    User Avatar
    Science Advisor

    Your teacher's point is that "f(x)= 0", for f a continuous function, is the boundary beween "f(x)> 0" and "f(x)< 0".
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook