# Inverse Z transform solution

1. Aug 15, 2007

### reinaldo

1. The problem statement, all variables and given/known data

i need to solve this 2 equations, got to find the inverse Z transform by partial fractions expension and long division method each, but in each one in none of the two methods match, and according to the teacher, they do match!...can anyone see if the do match? :surprised

2. Relevant equations

X(z)= ((z^2)-0.7z)/(z-1*z-0.6)

and

X(z)= (1+2z^-1)/(1-z^-1)^2

3. The attempt at a solution

2. Aug 15, 2007

### learningphysics

Did you do partial fraction in z or $$z^{-1}$$ ?

Remember that to use partial fraction you need the degree of the numerator< degree of the denominaotr (in whatever variable you choose z or $$z^{-1}$$)

Sometimes you can't use z because the degree of the numerator>= degree of the denominator so you can switch to $$z^{-1}$$ or vice versa... so you divide or multiply the numerator and denominator by a power of z to switch from one to the other...

But sometimes neither way works... degree of the numerator >=degree of the denominator with both ways... then you'll have to do one step of long division to get a remainder... so

P(z)/Q(z) = A(z) + R(z)/Q(z).... and now you can use partial fraction on R(z)/Q(z)...

But in both your problems, partial fractions in $$z^{-1}$$ should be no problem.