$\begin{equation*} \begin{cases} 5x - 4y = 1 &\\ 3x + 1 = 13 &\\ 7x - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x - 4y = 1 &\\ 3x = 13 - 1 &\\ 7x - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x - 4y = 1 &\\ 3x = 12 &\\ 7x - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x - 4y = 1 &\\ x = 4 &\\ 7x - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5 * 4 - 4y = 1 &\\ x = 4 &\\ 7 * 4 - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 20 - 4y = 1 &\\ x = 4 &\\ 28 - 5y = 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 4y = 20 - 1 &\\ x = 4 &\\ 5y = 28 - 1 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 4y = 19 &\\ x = 4 &\\ 5y = 27 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} y = 4,75 &\\ x = 4 &\\ y = 5,4 & \end{cases} \end{equation*}$
4,75 ≠ 5,4
Система уравнений не имеет решений.

$\begin{equation*} \begin{cases} 11x + 3y = 1 &\\ 2x + y = 3 &\\ 5x + 2y = 4 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 11x + 3y = 1 &\\ y = 3 - 2x &\\ 5x + 2y = 4 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 11x + 3(3 - 2x) = 1 &\\ y = 3 - 2x &\\ 5x + 2(3 - 2x) = 4 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 11x + 9 - 6x = 1 &\\ y = 3 - 2x &\\ 5x + 6 - 4x = 4 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x = 1 - 9 &\\ y = 3 - 2x &\\ x = 4 - 6 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 5x = -8 &\\ y = 3 - 2x &\\ x = -2 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} x = -1,6 &\\ y = 3 - 2x &\\ x = -2 & \end{cases} \end{equation*}$
−1,6 ≠ −2
Система уравнений не имеет решений.