Chapter 6 - Vector Spaces - 6.1 Vector Spaces and Subspaces - Exercises for 6.1 - Page 442: 52

$C$ is in the span of $A$ and $B$.

Since $$(-1)\begin{bmatrix} 1 & 1 \\ -1 & 1 \end{bmatrix} + 4\begin{bmatrix} 1 & -1 \\ 1 & 0 \end{bmatrix} = \begin{bmatrix} 3 & -5 \\ 5 & -1 \end{bmatrix} $$ $C$ is in the span of $A$ and $B$.