3) Take in consideration the following function f(x)=\left\{\begin{array}{ll}

f: \mathbb{R} \rightarrow \mathbb{R} & \\

\frac{x^{2}-4 x+\cos (\sin (x)),}{x^{4}+4 x^{2}+1}, & x \leq 0

\end{array}\right. a) Show that the function f is continuous in R+ and in R- but discontinuous in the point X b) Say justifying, if f is differenciable in X=0