Determine if the three matrices span the vector space of $2\times 2$ matrices Thus far I've seen vectors and polynomials but this the first and only exercise I find that introduces matrices.
The question is as follows:

Determine whether the three matrices 
$\begin{pmatrix}
    1 &  1 \\
    1 & 0\\ \end{pmatrix}$, $\begin{pmatrix}
    -1 &  0 \\
    0 & 1\\ \end{pmatrix}$, $\begin{pmatrix}
     0 &  1 \\
    1 & 2\\ \end{pmatrix}$
span the vector space of all 2x2 symmetric matrices.

I am stuck at this stage because previously I would find the matrix of the vectors or polynomials and work on that, but this time it's 3 matrices, what are the steps that I should follow to always get it right?

Take an arbitrary symmetric matrix
$$\begin{pmatrix} x & y \\ y & z \end{pmatrix}$$
and compute $a, b, c$ such that
\begin{align*}\begin{pmatrix} x & y \\ y & z \end{pmatrix} &= a\begin{pmatrix} 1 & 1 \\ 1 & 0 \end{pmatrix} + b\begin{pmatrix} -1 & 0 \\ 0 & 1 \end{pmatrix} + c\begin{pmatrix} 0 & 1 \\ 1 & 2 \end{pmatrix} \\
&= \begin{pmatrix} a - b & a + c \\ a + c & b + 2c \end{pmatrix}.
\end{align*}
Equating entries, this produces the system of linear equations,
\begin{align*}
a - b &= x \\
a + c &= y \\
b + 2c &= z,
\end{align*}
which can be solved using whichever methods you like. Either way, we get
\begin{align*}
a &= -x + 2y - z \\
b &= -2x + 2y - z \\
c &= x - y + z.
\end{align*}
In particular, at least one solution exists regardless of the value of $x, y, z$. That is, the arbitrary symmetric matrix is spanned by the the three matrices.
