Laplace Transform#

Definition#

\[\displaystyle F(s) = \Laplace{f(t)}(s)=\int_0^\infty e^{-st} f(t) \dt\]

Properties#

  1. \(\displaystyle \Laplace{f+g} = \Laplace{f} + \Laplace{g}\).

  2. \(\displaystyle \Laplace{cf} = c\Laplace{f}\) for any constant \(c\).

  3. \(\displaystyle \Laplace{e^{at}f(t)}(s)=F(s-a)\).

  4. \(\displaystyle \Laplace{f'}(s)=sF(s) - f(0)\).

  5. \(\displaystyle \Laplace{f''}(s)=s^2F(s) -sf(0)- f'(0)\).

Table of Laplace Transforms#

\(f(t)\)

\(F(s)=\Laplace{f}(s)\)

\(1\)

\(\dfrac{1}{s}\), \(\quad s>0\)

\(e^{at}\)

\(\dfrac{1}{s-a}\), \(\quad s>a\)

\(t^n\)

\(\dfrac{n!}{s^{n+1}}\), \(\quad s>0\) , \(\quad n=1,2,\ldots\)

\(\sin bt\)

\(\dfrac{b}{s^2+b^2}\), \(\quad s>0\)

\(\cos bt\)

\(\dfrac{s}{s^2+b^2}\), \(\quad s>0\)

\(e^{at} t^n\)

\(\dfrac{n!}{(s-a)^{n+1}}\), \(\quad s>a\), \(\quad n=1,2,\ldots\)

\(e^{at} \sin bt\)

\(\dfrac{b}{(s-a)^2+b^2}\), \(\quad s>a\)

\(e^{at} \cos bt\)

\(\dfrac{s-a}{(s-a)^2+b^2}\), \(\quad s>a\)

\(\sinh bt\)

\(\dfrac{b}{s^2-b^2}\)

\(\cosh bt\)

\(\dfrac{s}{s^2-b^2}\)

Inverse Laplace Transform#

\[f(t) = \invLaplace{F(s)}(t)\]