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Homework Help: Z transform question.

  1. Dec 9, 2006 #1
    1. The problem statement, all variables and given/known data
    consider the difference equation
    x(n+2)-0.3679x(n+1)+0.3679x(n)=0.3679u(n+1)+u(n)
    where u(n) is the input and given by
    u(n)=0 n<0
    u(0)=1
    u(1)=0.2142
    u(2)=-0.2142
    u(n)=0 n=3,4,5.......
    determine the output x(n)





    3. The attempt at a solution
    let A=0.3679 and B=0.3642
    i took z transform for both sides so it became.
    z^2 x(z)-z^2x(0)-zx(1)-A[zx(z)-zx(0)]+Ax(z)=A[zu(z)-zu(0)]+Bu(z)
    x(z)[z^2-Az+A]+x(0)[Az-z^2]-zx(1)=A[zu(z)-zu(0)]+Bu(z)
    x(z)[z^2-Az+A]=A[zu(z)-zu(0)]+Bu(z)-x(0)[Az-z^2]+zx(1)

    then what can i do?
    also how can i make use of u(1)=0.2142
    u(2)=-0.2142
    i am too confused and need help.
     
  2. jcsd
  3. Dec 9, 2006 #2
    To solve the problem, you need to specify some initial conditions. As it stands, it's unsolvable.
     
  4. Dec 9, 2006 #3
    this is the full question given to me to solve and i am sure it is complete.
     
  5. Dec 26, 2006 #4
    late reply ,, have you known the correct solution ?

    the key that the input is not a step function , u have to use the u(0) , u(1) ... etc to draw the input and find expression to it .
     
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