1. **Problem Statement:** Find the z-transform of the given functions:
(i) $$F(s) = \frac{1}{(s+a)^2}$$
(ii) $$F(s) = \frac{10(1-e^{-s})}{s(s+2)}$$
2. **Recall the z-transform definition:**
The z-transform of a discrete-time signal $x[n]$ is defined as:
$$X(z) = \sum_{n=0}^\infty x[n] z^{-n}$$
However, here we are given Laplace domain functions $F(s)$, so we need to relate the Laplace transform to the z-transform.
3. **Relation between Laplace and z-transform:**
If $s = \frac{1}{T} \ln z$, where $T$ is the sampling period, then the z-transform can be related to the Laplace transform by substituting $s$ accordingly.
4. **(i) For** $$F(s) = \frac{1}{(s+a)^2}$$
This is the Laplace transform of the function $f(t) = t e^{-a t} u(t)$, where $u(t)$ is the unit step.
The discrete-time sequence sampled at $t = nT$ is:
$$x[n] = n T e^{-a n T}$$
The z-transform is:
$$X(z) = \sum_{n=0}^\infty n T e^{-a n T} z^{-n}$$
Rewrite $e^{-a T} = r$, then:
$$X(z) = T \sum_{n=0}^\infty n (r z^{-1})^n$$
Using the formula for the sum:
$$\sum_{n=0}^\infty n x^n = \frac{x}{(1-x)^2}$$ for $|x|<1$,
we get:
$$X(z) = T \cdot \frac{r z^{-1}}{(1 - r z^{-1})^2} = \frac{T r z^{-1}}{(1 - r z^{-1})^2}$$
5. **(ii) For** $$F(s) = \frac{10(1-e^{-s})}{s(s+2)}$$
Rewrite numerator:
$$1 - e^{-s}$$ corresponds to a difference in Laplace domain, which relates to a discrete difference in time domain.
We can write:
$$F(s) = 10 \left( \frac{1}{s(s+2)} - \frac{e^{-s}}{s(s+2)} \right)$$
The inverse Laplace of $$\frac{1}{s(s+2)}$$ is:
$$f_1(t) = \frac{1}{2} t - \frac{1}{2} + \frac{1}{2} e^{-2 t}$$
The term $$e^{-s}$$ corresponds to a delay of 1 unit in time, so:
$$f_2(t) = f_1(t-1) u(t-1)$$
Therefore, the time domain function is:
$$f(t) = 10 (f_1(t) - f_1(t-1) u(t-1))$$
Sampling at $t = nT$ and taking the z-transform:
$$X(z) = 10 \left( X_1(z) - z^{-1} X_1(z) \right) = 10 X_1(z) (1 - z^{-1})$$
Where $X_1(z)$ is the z-transform of $f_1(nT)$.
The z-transform of $f_1(nT)$ can be computed by known transforms or numerical methods depending on $T$.
**Final answers:**
(i) $$X(z) = \frac{T e^{-a T} z^{-1}}{(1 - e^{-a T} z^{-1})^2}$$
(ii) $$X(z) = 10 X_1(z) (1 - z^{-1})$$ where $X_1(z)$ is the z-transform of $f_1(nT) = \frac{1}{2} n T - \frac{1}{2} + \frac{1}{2} e^{-2 n T}$.
Z Transform Functions 3865C7
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