Hola espero su ayuda en lo siguiente:
Si \( f(x)=\displaystyle\dfrac{4}{\pi}\sum_{k=0}^{\infty}\dfrac{(-1)^k}{2k+1}\mathrm{exp}\{-\pi^2(2k+1)^2/(8x^2)\}\;\;\forall x>0 \), entonces
\( (\displaystyle\frac{4}{\pi }\mathrm{exp}\left\{-\frac{{\pi }^{2}}{8{x}^{2}}\right\}-\frac{4}{3\pi }\mathrm{exp}\left\{-\frac{9{\pi }^{2}}{8{x}^{2}}\right\})\le f(x)\le \frac{4}{\pi }\mathrm{exp}\left\{-\frac{{\pi }^{2}}{8{x}^{2}}\right\}, \forall x>0 \)
