Wednesday, October 18, 2017

integration - $intlimits_0^{10}e^{-0.04t}cdot e^{-0.001t^2}dt$

I need to find the following integral




$$\int\limits_0^{10}e^{-0.04t ~-0.001t^2}dt$$
This integral seems to "scream" for the error function, but I have never worked with the error function yet, so I have no idea how to do this. Can anyone please show me how this definite integral can be determined?



Update:
After following the hints given, I have the following:



\begin{align}\int\limits_0^{10}e^{\frac{-1}{1000}(t^2+40t)}dt &= e^{\frac{400}{1000}}\int\limits_0^{10} e^{\frac{-1}{1000}(t+20)^2}dt\end{align}



Now, let $u = t+20$, then our integral changes to

\begin{align*}e^{\frac{400}{1000}}\int\limits_{20}^{30}e^{\frac{-1}{1000}u^2}du\end{align*}
I am stuck here though, since I only know how to use the error function of $\int_0^xe^{-at^2}dt$, which is different from what I have, since the lower limit is not zero? Please help!

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