integrating this infinite gaussian integral How does one integrate 
$\int_{-\infty}^{+\infty}x e^{-\lambda ( x-a )^2 }dx $
where $\lambda$ is a positive constant.
My integral tables are not returning anything useable. The best it return is non-definite gaussian integrals. Useless!
Help please

If the integral follows the comments above here is a hint.
$$
\int_{-\infty}^{\infty} x\mathrm{e}^{-\lambda(x-a)^2}dx
$$
let $\lambda(x-a)^2 = \frac{z^2}{2}\to z=\sqrt{2\lambda}(x-a)$ 
we get
$$
\frac{1}{\sqrt{2\lambda}}\int_{-\infty}^{\infty}\left(\frac{z}{\sqrt{2\lambda}}+a\right)\mathrm{e}^{-\frac{z^2}{2}}dz
$$
