73. Solve the system of equations

$$
\left\{\begin{array}{l}
2 x-3 y=11 \\
6 x-9 y=33
\end{array}\right.
$$
solution. We find

$\Delta=\left|\begin{array}{ll}2 & -3 \\ 6 & -9\end{array}\right|=0, \Delta_{x}=\left|\begin{array}{ll}11 & -3 \\ 33 & -9\end{array}\right|=0 ; \Delta_{y}=\left|\begin{array}{ll}2 & 11 \\ 6 & 33\end{array}\right|=0$.

This system has an infinite number of solutions (the coefficients of the unknowns are proportional).