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Math Help - Matrix and Vectors

  1. #1
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    Matrix and Vectors

    A = 2 1..............b = 3
    ......4 3...................4


    Given the matrix A and vector b and an unknown vector x

    such that x = x1
    ...................x2

    expand as a set of equations and solve them to find x



    Ive been tryng to do this using 'Gaussian Elimination' using the upper triangular matrix form, i can figure out 'x2' as being '-2', but i just cant figure out how to get 'x1' which is '5/2'.

    Ive asked for help in other places but they seem very eager to offer answers with no working out or methods whatsoever so its of no help to me. If i can figure this out, ill be able to answer the one that will up on my exam paper on Tuesday >.<

    Thanks for reading
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  2. #2
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    A = 2 1.....x = x_1.......b = 3
    ......4 3..........x_2............4

    [A][x] = [b]

    row times column ...

    2x_1 + 1x_2 = 3
    4x_1 + 3x_2 = 4

    x_2 = -2

    substitute x_2 = -2 in either equation ...

    2x_1 + (-2) = 3
    2x_1 = 5
    x_1 = 5/2

    4x_1 + 3(-2) = 4
    4x_1 = 10
    x_1 = 5/2
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  3. #3
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    Thank you
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