Question

Which of the following statements is true about the two sided Laplace transform?

Options :

  1. It exists for every signal that may or may not have a Fourier Transform.

  2. It has no poles for any bounded signal that is non-zero only inside a finite time interval.

  3. If a signal can be expressed as a weighted sum of shifted one sided exponentials, then its Laplace
    transform will have no poles.

  4. The number of finite poles and finite zeroes must be equal.

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Answer :

It has no poles for any bounded signal that is non-zero only inside a finite time interval.

Solution :

From the properties of ROC of Laplace transform :
1. ROC does not contain any pole
2. ROC of transform of a bounded finite duration signal is entire S-plane
It can be said that, if a signal is bounded and exists only for finite duration, then ROC is entire s-plane, so
it can not have any pole as ROC does not contain any pole.
Hence, the correct option is (B)

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