%\documentclass{article}
%\usepackage[english]{babel}
%\usepackage{amsmath}
%\begin{document}
\begin{equation}
f(T) = 
\begin{cases}
0 & \text{if} \quad T < 273K \\
1 - \dfrac{(T_{max} - T)^2}{(T_{max} - T_{min})^2} & \text{if} \quad 273K \leq T \leq 293K \\
1 & \text{if} \quad T > 293K
\end{cases} %\]
\end{equation}
where : \\
\begin{itemize}
 \item  $ T_{min} = 273K$ 
 \item  $ T_{max} = 293K$
\end{itemize}
%\end{document}
