Results 1 to 3 of 3

Math Help - Could you please double-check my work

  1. #1
    Newbie
    Joined
    Nov 2007
    Posts
    9

    Could you please double-check my work

    My answers are in bold text.

    1. Problem: |7 - x | = 9

    |7 - x| = 9....................|7 - x | = -9

    |x| = 9 - 7....................|x| = -9 -7

    |x| = -2........................|x| = -16


    2. Problem: 3 |x - 2| + 4 = 13

    |3x - 6| + 4 = 13.............................. 3|x - 2| + 4 = 13

    |3x - 6| = 13 - 4...............................3|x - 2| = 13 -9

    |3x - 6| = 9.......................................|x - 2| = 3

    |3x| = 9 + 6.......................................x - 2 = -3

    |3x| = 15...........................................x = 2 + (-3)

    X = 5...............................................x = -1



    3. Problem: 2x + 8 < 14

    2x < 14 - 8

    2x < 6
    2......2

    x < 3


    4. Problem: 11 > 5y - 9

    11 + 9 > 5y

    20 > 5y
    5......5

    4 > y


    5. Problem: 5x - 9> - 3 +4x

    5x - 4x > - 3 + 9

    x > 6


    Thanks!
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Forum Admin topsquark's Avatar
    Joined
    Jan 2006
    From
    Wellsville, NY
    Posts
    9,939
    Thanks
    338
    Awards
    1

    Post

    Quote Originally Posted by slykksta View Post
    3. Problem: 2x + 8 < 14

    2x < 14 - 8

    2x < 6
    2......2

    x < 3


    4. Problem: 11 > 5y - 9

    11 + 9 > 5y

    20 > 5y
    5......5

    4 > y


    5. Problem: 5x - 9> - 3 +4x

    5x - 4x > - 3 + 9

    x > 6
    These are correct.

    For the first two the method is not right.
    |7 - x| = 9

    There are two ways to approach this. The first is to square both sides of the equation, thereby getting rid of the absolute value bars. (This is my choice of technique.) Or you can note that when 7 - x is positive that the equation reads 7 - x = 9, and when 7 - x is negative then the equation reads -(7 - x) = 9. Between the two of these you will find either no, 1 or 2 solutions.

    Let me do this one the last way:
    |7 - x| = 9

    Assume 7 - x > 0

    Then
    7 - x = 9 \implies x = -2.

    Now assume 7 - x < 0:

    Then
    -(7 - x) = 9 \implies x = 16

    So your two solutions are x = -2 and x = 16.

    Try #2 again.

    -Dan
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Super Member angel.white's Avatar
    Joined
    Oct 2007
    Posts
    723
    Awards
    1
    For yourself, you can check your answers by plugging them back into the origional equation, if the two sides are equal, your answer is correct. If not, you need to figure out where you went wrong. This is especially helpful for tests.
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. [SOLVED] Double check my work?
    Posted in the Calculus Forum
    Replies: 1
    Last Post: February 15th 2010, 05:31 PM
  2. Double check my Work problem.
    Posted in the Calculus Forum
    Replies: 0
    Last Post: December 7th 2008, 10:01 PM
  3. Could you please double-check my work
    Posted in the Algebra Forum
    Replies: 2
    Last Post: November 15th 2007, 04:46 PM
  4. Can someone double check my work? conics
    Posted in the Pre-Calculus Forum
    Replies: 1
    Last Post: November 22nd 2006, 08:53 AM
  5. derivatives - double check my work please
    Posted in the Calculus Forum
    Replies: 3
    Last Post: May 23rd 2006, 01:19 PM

Search Tags


/mathhelpforum @mathhelpforum