Prove that $\|_{2}(R)$, the set of all $2 \times 2$ matrices of real numbers, with matrix addition and the scalar multiplication
$$
k\left(\begin{array}{ll}
a & b \\
c & d
\end{array}\right)=\left(\begin{array}{ll}
k a & k b \\
k c & k d
\end{array}\right)
$$
is a vector space over $\mathbb{R}$.