And now for the definitive answer....
Begin with the original equation s^2/(s^4 - 9), which breaks down into (s/(s^2 + 3))*(s/(s^2 - 3)). The inverse Laplace of s/(s^2 + 3) is cos (3t) and the inverse Laplace of s/(s^2 - 3) is cosh (3t), therefore...
...the inverse Laplace transform of the original equation is cos(3t) * cosh (3t), taking advantage of the convolution theorem. Of course, s > abs(sqrt(3)).
That should end the disussion. [img]graemlins/petard.gif[/img]
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