How to write the piecewise equation in latex?

When you are writing a paper, especially with a lot of mathematical equations, like piecewise equation, to know some ways to achieve this is quite a fun. To myself, I prefer using "cases environment" . Feel free to take place "\[ ... \]" by "\begin{equation}...\end{equation}"  

The cases environment

The cases environment^[1] allows the writing of piecewise functions:

\[  u(x) =   \begin{cases}    \exp{x} & \text{if } x \geq 0 \\    1       & \text{if } x < 0   \end{cases} \]

More information about editing advanced math in Latex can be referred here!