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Solve system of equations using laplace transform and evaluate x(1)

  1. Oct 30, 2014 #1
    1. The problem statement, all variables and given/known data
    I keep getting the wrong answer, and wolphram seems to back me up.

    Here's the system of equations

    ##(-10+s)X(s)-7Y(s)=\frac{10}{s}##
    ##X(s)+(-2+s)Y(s)=0##

    2. Relevant equations


    3. The attempt at a solution
    Using Cramer's rule I've got

    ##X(s)=\frac{10}{(s-9)(s-3)}-\frac{20}{s(s-9)(s-3)}##
    Using partial fraction decomposition I've got

    ##x(t)=e^{9t}(10/6-20/54)+e^{3t}(-10/6+20/18)-20/27##

    Evaluating ##x(1)## I get ##10492.1##
     
  2. jcsd
  3. Oct 31, 2014 #2

    Ray Vickson

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    Your answer is correct. What makes you think it is wrong?
     
  4. Oct 31, 2014 #3
    The correct answer is supposedly -1426.16 :/ Strangely enough, if I solve ##y## and evaluate ##y(1)## I get an answer close to that.
     
  5. Oct 31, 2014 #4

    Ray Vickson

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    If you typed out the equations correctly, your solution is correct. So, either you mis-represented the problem, or the supposed answers are wrong.
     
  6. Oct 31, 2014 #5
    Thanks for the help.
     
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