Show that if $T$ is a linear transformation from a vector space $\mathcal{U}$ over $\mathbb{F}$ with basis $\left\{\mathbf{u}_1, \ldots, \mathbf{u}_q\right\}$ into a vector space $\mathcal{V}$ over $\mathbb{F}$ with basis $\left\{\mathbf{v}_1, \ldots, \mathbf{v}_p\right\}$, then there exists a unique set of scalars $a_{i j} \in \mathbb{F}, i=1, \ldots, p$ and $j=1, \ldots, q$ such that
$$
T \mathbf{u}_j=\sum_{i=1}^p a_{i j} \mathbf{v}_i \text { for } j=1, \ldots, q
$$
and hence that
$$
T\left(\sum_{j=1}^q x_j \mathbf{u}_j\right)=\sum_{i=1}^p y_i \mathbf{v}_i \Longleftrightarrow A \mathbf{x}=\mathbf{y}
$$
where $\mathbf{x} \in \mathbb{F}^q$ has components $x_1, \ldots, x_q, \mathbf{y} \in \mathbb{F}^p$ has components $y_1, \ldots, y_p$ and the entries $a_{i j}$ of $A \in \mathbb{F}^{p \times q}$ are determined by formula (1.5).