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August 20th, 2015, 03:54 PM  #1 
Senior Member Joined: Aug 2014 From: United States Posts: 137 Thanks: 21 Math Focus: Learning  Inverse Laplace Transform/Complex Integral
I found what appears to be a definition of the inverse Laplace Transform which is as follows: $\displaystyle f(t)=\frac{1} {2\pi i} \lim\limits_{T\to\infty} \int_{\sigmaiT}^{\sigma+iT} e^{st} \mathscr L \{f(t)\} \, ds$ I began trying to prove that the above is true. This reduces to proving that $\displaystyle f(t)=\frac{1} {2\pi i} \lim\limits_{T\to\infty} \int_{\sigmaiT}^{\sigma+iT} \int_0^\infty f(t)\,dt\,ds$ I don't know where to continue from here. I know I'm done by the Cauchy Integral Formula if I can prove that $\displaystyle\lim\limits_{T\to\infty} \int_{\sigmaiT}^{\sigma+iT}\int_0^\infty f(t)\,dt\,ds=\oint_{\gamma} \frac{f'(z)} {zt}\,dz$ where $\gamma$ is some contour in the complex plane whose interior region contains $t$ and is traversed counterclockwise. However, at the moment I am stuck and do not know how to continue. Any thoughts? Note: The definition I am using for the Laplace Transform is $\displaystyle \mathscr L\{f(t)\}=\int_{0}^\infty e^{st} f(t)\,dt$ 

Tags 
integral, inverse, laplace, transform or complex 
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