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Math Help - URGENT!

  1. #1
    Junior Member
    Joined
    Oct 2008
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    Unhappy URGENT!

    If A=
    | |
    | 5 e5 t sin(4 t) −5 e2 t cos(4 t)|
    | |
    | |
    | −6 e5 t cos(4 t) −6 e2 t sin(4 t)|

    then A^−1 is?

    I need to find the inverse matrix of A, (A^-1) i've done it several times and have gotten the wrong answer (obviously, or i wouldn't be on here)
    It's a homework quiz online that's due this evening, any help would be wonderful. thank you all
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  2. #2
    is up to his old tricks again! Jhevon's Avatar
    Joined
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    Quote Originally Posted by williamb View Post
    If A=
    | |
    | 5 e5 t sin(4 t) −5 e2 t cos(4 t)|
    | |
    | |
    | −6 e5 t cos(4 t) −6 e2 t sin(4 t)|

    then A^−1 is?

    I need to find the inverse matrix of A, (A^-1) i've done it several times and have gotten the wrong answer (obviously, or i wouldn't be on here)
    It's a homework quiz online that's due this evening, any help would be wonderful. thank you all
    do you mean A = \left( \begin{array}{cc}  5e^{5t} \sin 4t & -5e^{2t} \cos 4t \\ & \\ -6e^{5t} \cos 4t & -6e^{2t} \sin 4t \end{array} \right) ?

    obviously, since this is for a quiz we can't tell you the answer, but if the above is your matrix, note that following (which should be in your text):

    if M =  \left( \begin{array}{cc}  a & b \\ c & d \end{array} \right), then M^{-1} = \frac 1{ad - bc}  \left( \begin{array}{cc} d & -b \\ -c & a \end{array} \right) =  \left( \begin{array}{cc} \frac d{ad - bc} & \frac {-b}{ad - bc} \\ & \\ \frac {-c}{ad - bc} & \frac a{ad - bc} \end{array} \right), provided M is invertible, that is, its determinant ad - bc is not zero
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