Differentiability at a Point

Consider the piecrwise$-$defined fatction:

$f(x)=\{\begin{array}{ccc}{x}^2,& if& x1\\ 2x-1,& if& x>1\end{array}$

$($a$)$ Is $f(x)$ condinuous at $x=1?$ Show your reasoning,

$($b$)$ Is $f(x)$ differentiable at $x=17$ Use the definition of the derivative from both was to luatly.