Results 1 to 3 of 3

Math Help - I must be making a simple mistake here.

  1. #1
    Newbie
    Joined
    Mar 2010
    Posts
    1

    I must be making a simple mistake here.

    Ok the problem is,
    Given:

    |r s t|
    |u v w| = 4
    |x y z|

    Evaluate:

    |-x -y -z|
    |r s t|
    |u v w|

    My steps at finding the solution are:
    1.
    |r s t|
    (-)|-x -y -z|
    |u v w|

    2.
    |r s t|
    (-)(-)|u v w|
    |-x -y -z|

    3.
    |r s t|
    (-)(-)(-1)|u v w|
    |x y z|

    4. (-)(-)(-1)(4)= -4

    Which for some reason is wrong because I am supposed to show that it equals 4 not -4. What am I doing wrong?
    Follow Math Help Forum on Facebook and Google+

  2. #2
    Senior Member Tinyboss's Avatar
    Joined
    Jul 2008
    Posts
    433
    It's two row swaps, and a row multiplication by -1, so your answer looks right to me.
    Follow Math Help Forum on Facebook and Google+

  3. #3
    Banned
    Joined
    Oct 2009
    Posts
    4,261
    Thanks
    2
    Quote Originally Posted by qwerty11 View Post
    Ok the problem is,
    Given:

    |r s t|
    |u v w| = 4
    |x y z|

    Evaluate:

    |-x -y -z|
    |r s t|
    |u v w|

    My steps at finding the solution are:
    1.
    |r s t|
    (-)|-x -y -z|
    |u v w|

    2.
    |r s t|
    (-)(-)|u v w|
    |-x -y -z|

    3.
    |r s t|
    (-)(-)(-1)|u v w|
    |x y z|

    4. (-)(-)(-1)(4)= -4

    Which for some reason is wrong because I am supposed to show that it equals 4 not -4. What am I doing wrong?


    How did you get to \begin{pmatrix}\!\!-x&\!\!-y&\!\!-z\\r&s&t\\u&v&w\end{pmatrix} from the original matrix ?

    First, you interchanged the 2nd and 3rd rows, and thus the determinant is multiplied by -1, and then you interchanged the 1st and 2nd rows and again the det. gets multiplied by -1, so we still have the original determinant. But now you multiplied the first row by -1 and thus the det. of the new matrix equals -4 ...
    Thus you're right: it is -4


    Tonio
    Follow Math Help Forum on Facebook and Google+

Similar Math Help Forum Discussions

  1. what is the mistake here
    Posted in the Calculus Forum
    Replies: 16
    Last Post: July 2nd 2011, 03:19 PM
  2. Maple making mistake?
    Posted in the Math Software Forum
    Replies: 3
    Last Post: April 3rd 2010, 03:28 PM
  3. Limit question, likely a simple mistake on my part.
    Posted in the Pre-Calculus Forum
    Replies: 3
    Last Post: March 29th 2010, 11:49 PM
  4. making equations of simple harmonic functions.and.?
    Posted in the Trigonometry Forum
    Replies: 1
    Last Post: January 24th 2009, 04:13 AM
  5. Replies: 3
    Last Post: September 23rd 2008, 08:44 AM

Search Tags


/mathhelpforum @mathhelpforum