\begin{definition}[Definition:Are]
The '''are''' is a derived unit of area.
One '''are''' is equal to a square whose side measures $10$ metres.
{{begin-eqn}}
{{eqn | o = 
      | r = 1
      | c = '''are'''
}}
{{eqn | r = 100
      | c = square metres
}}
{{eqn | o = \approx
      | r = 119 \cdot 60
      | c = square yards
}}
{{end-eqn}}
\end{definition}