Math

<math>\tau</math>

<math>
 \operatorname{erfc}(x) =
 \frac{2}{\sqrt{\pi}} \int_x^{\infty} e^{-t^2}\,dt =
 \frac{e^{-x^2}}{x\sqrt{\pi}}\sum_{n=0}^\infty (-1)^n \frac{(2n)!}{n!(2x)^{2n}}
</math>