I'm trying to study Linear Algebra :) In my textbook, the author said $\begin{align} u_1=\begin{pmatrix}1 & 0 & 1 & 0 & -1\end{pmatrix} \end{align}$ $\begin{align} x_1=\begin{pmatrix}-1 \\ -2 \\ 1 \\ 0 \\ 0\end{pmatrix} \end{align}$ $\begin{align} u_1 \cdot x_1 = 0 \end{align}$
However, I can't understand how I can do dot product with $u_1$ and $v_1$.
The form of $u_1$ is horizontally stretched, but $v_1$ is vertically stretched. Isn't it violating the definition of dot product of matrices?