Graphs of Piecewise Functions

$f(x)=\begin{matrix}3&if& x\geq0\end{matrix}$

$f(x)=\begin{matrix}3&if& x\leq0\end{matrix}$

$f(x)=\begin{matrix}e^x&if&x>0\end{matrix}$

$f(x)=\begin{matrix}3&if& x<0\end{matrix}$

$f(x)=\begin{matrix}x^2&if&x>0\end{matrix}$