# Poles of laplace transform

1. Jul 14, 2009

### khdani

Hello,
if i said that x(t) is real,
why X(s) must occur in conjugate reciprocal pairs ?

2. Jul 16, 2009

### CEL

It does not.
If $$x(t) = e^{at}$$, then $$X(s) = \frac{1}{s-a}$$, wich has a real pole at s = a.
In the other way, if x(t) is a sinusoid, then X(s) will have complex conjugate poles.