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Math Help - solving simultaneous linear eqns

  1. #1
    Member maybeline9216's Avatar
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    Question solving simultaneous linear eqns

    Solve, using matrices, the pair of simultaneous linear eqns,

    3x= 2y + 8
    14= 5x -4y
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  2. #2
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    Quote Originally Posted by maybeline9216 View Post
    Solve, using matrices, the pair of simultaneous linear eqns,

    3x= 2y + 8
    14= 5x -4y
    Re-write:

    3x - 2y = 8

    5x - 4y = 14

    Can you construct the matrix equation from this?
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  3. #3
    Member maybeline9216's Avatar
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    Question

    yea but my answer is so big x=30,y=41 and my solution just works for the first eqn.

    the paper's answer is x=2 y=-1

    i dunno where went wrong but from these 2 simultaneous qns :

    3x-2y=8 -(1)
    5x-4y=14

    im wondering do u nid to do something to them[like (1)x2?] or u can just straight-away write out the matrix from there??
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  4. #4
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    Quote Originally Posted by maybeline9216 View Post
    yea but my answer is so big x=30,y=41 and my solution just works for the first eqn.

    the paper's answer is x=2 y=-1

    i dunno where went wrong but from these 2 simultaneous qns :

    3x-2y=8 -(1)
    5x-4y=14

    im wondering do u nid to do something to them[like (1)x2?] or u can just straight-away write out the matrix from there??
    \begin{bmatrix}3 & -2\\5& -4\end{bmatrix} \, \begin{bmatrix}x \\ y \end{bmatrix} = \begin{bmatrix}8 \\ 14 \end{bmatrix}

    which has the form AX = B. Left multiply both sides by the inverse of matrix A to solve for X. The solution to the equations is the matrix elements of X.
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  5. #5
    Member maybeline9216's Avatar
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    Question

    I did the same mtd as you.... my matrix is same as yours too....but my answer is different
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  6. #6
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    Quote Originally Posted by maybeline9216 View Post
    I did the same mtd as you.... my matrix is same as yours too....but my answer is different
    What do you get for the inverse matrix A^{-1}? What do you get for the product A^{-1} B?
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  7. #7
    Member maybeline9216's Avatar
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    Quote Originally Posted by mr fantastic View Post
    What do you get for the inverse matrix A^{-1}? What do you get for the product A^{-1} B?
    i got [ 2 -1 ] as my inverse matrix
    [ 2.5 -1.5 ]

    P.S i dunno hw to use latex, pls bear with me...

    and i got [30] as my( A^-1)(B)
    [41]
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  8. #8
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    Quote Originally Posted by maybeline9216 View Post
    i got [ 2 -1 ] as my inverse matrix
    [ 2.5 -1.5 ]

    P.S i dunno hw to use latex, pls bear with me...

    and i got [30] as my( A^-1)(B)
    [41]
    Your inverse A^{-1} is correct, your product A^{-1} B is wrong.

    The first entry in the product is 16 - 14 = 2, NOT 16 + 14 = 30 ....
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  9. #9
    Member maybeline9216's Avatar
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    thanks lots=) i found out where im careless already!!!
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