Results 1 to 3 of 3

Math Help - Adding and Subtracting Matrices

  1. #1
    Newbie
    Joined
    Nov 2011
    Posts
    1

    Adding and Subtracting Matrices

    I've got this problem from my SAT Math level 2 prep book, which I think has the wrong answer.

    The question is: Adding and Subtracting Matrices-img-20111108-00174.jpg


    So what I did was subtract the matrix on the right by the left, and then both multiply both sides by -1.

    The answer I get is
    (-4 1 -11)
    8 -1 -2


    However in the book, the answer says b)Adding and Subtracting Matrices-img-20111108-00175.jpgAdding and Subtracting Matrices-img-20111108-00176.jpg



    I have never done matrices before reading this book, and I'm trying to learn from the book. This is proving difficult as this book is quite hard to read, although I correctly answered the previous questions.
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Super Member

    Joined
    May 2006
    From
    Lexington, MA (USA)
    Posts
    11,547
    Thanks
    539

    Re: Adding and Subtracting Matrices

    Hello, fobbz!

    Solve for X:\;\;\begin{pmatrix} 1&2&3 \\ 2&1&3\end{pmatrix} - X \;=\;\begin{pmatrix}5&1&8 \\ \text{-}6&0&5\end{pmatrix}

    We have: . X \;=\;\begin{pmatrix} 1&2&3 \\ 2&1&3\end{pmatrix} - \begin{pmatrix} 5&1&8\\ \text{-}6&0&5\end{pmatrix}

    Therefore: . X \;=\;\begin{pmatrix}\text{-}4 & 1 & \text{-}5 \\ 8 & 1 & \text{-}2\end{pmatrix}

    Follow Math Help Forum on Facebook and Google+

  3. #3
    MHF Contributor

    Joined
    Mar 2011
    From
    Tejas
    Posts
    3,150
    Thanks
    591

    Re: Adding and Subtracting Matrices

    because matrix arithmetic involves a lot of arithmetic operations "all at once", it is not uncommon to make various sign errors or other simple arithmetic mistakes in the process of doing one's calculations. i should know, this happens to me all the time.

    so one must be extra vigilant in checking and re-checking your work.

    it seems clear that what happened, is you added 8, instead of subtracting it (in the upper-right hand corner), other than that, everything is fine. your logic was fine, there was an error in execution (a sign error).
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. Adding and Subtracting Radicals
    Posted in the Algebra Forum
    Replies: 6
    Last Post: February 12th 2011, 08:12 AM
  2. Adding and subtracting negatives
    Posted in the Algebra Forum
    Replies: 2
    Last Post: January 6th 2011, 05:28 AM
  3. Adding and Subtracting Polynomials?
    Posted in the Algebra Forum
    Replies: 3
    Last Post: December 15th 2009, 01:34 PM
  4. adding and subtracting fractions
    Posted in the Algebra Forum
    Replies: 7
    Last Post: September 18th 2009, 08:10 AM
  5. adding and subtracting
    Posted in the Trigonometry Forum
    Replies: 4
    Last Post: December 6th 2008, 11:07 AM

Search Tags


/mathhelpforum @mathhelpforum