## Differentiable and Find df(x)

Let f: $R^n \rightarrow R$ be given by f(x) = $|x|^2$ = $\sum (x_j)^2$, where j = 1,...,n and x = ( $x_1$,..., $x_n$). Show that f is differentiable at all points in $R^n$. For each x $\in R^n$ find df(x)