$$u(t)$$ represents the unit step function. The Laplace transform of $$u\left( {t - \tau } \right)$$ is

The laplace transform of a function $$f(t)$$ is defined by
$$F\left( s \right) = L\left\{ {f\left( t \right)} \right\} = \int\limits_0^\infty {{e^{ - st}}f\left( t \right)dt.} $$.
Find the inverse laplace transform of $$F(s-a)$$

Find $$L\left\{ {{e^{at}}\,\cos \,\omega t} \right\}$$ when
$$L\left\{ {\cos \,\,\omega t} \right\} = {s \over {{s^2} + {\omega ^2}}}$$