Solution (source code)

= Solution

With the stated negative sign in the forward exponential, the <inverse Fourier transform> is
$$
\boxed{f(x)=\frac1{2\pi}\int_{-\infty}^{\infty}\widetilde f(k)e^{ikx}\,dk.}
$$
For example, this holds pointwise for <Schwartz functions>; more general square-integrable functions use the corresponding mean-square interpretation.