---
title: Pandoc-eqnos Demo
...

The equation for a straight line is
$$ y = mx + b $$ {#eq:line}
and the equation for a  polynomial is
$$ y = \sum_{n=0}^{\infty} a_n x^n $$ {#eq:polynomial}

Equation @eq:line and eq. @eq:polynomial are known to all first-year math students.

The Fourier series is a little more advanced:
$$ y = \frac{1}{2}a_0 + \sum_{n=1}^{\infty}a_n\cos(nx)
                      + \sum_{n=1}^{\infty}b_n\cos(nx)
$$ {#eq:fourier}

Equations {@eq:line}--{@eq:fourier} are used throughout science and engineering.

Equations can be left unnumbered if we do not need to refer to them:
$$ y = A e^{-\gamma t}\cos(2\pi f t) $$

It is also possible to number equations generically without planning to refer to them; e.g.:
$$ \pi = 3.141592653589793238462643 \ldots $$ {#eq:}