$\begin{equation*} \begin{cases} x - 6y = 17 &\\ 5x + 6y = 13 & \end{cases} \end{equation*}$
x − 6y + 5x + 6y = 17 + 13
6x = 30
x = 5
5 − 6y = 17
−6y = 17 − 5
−6y = 12
y = −2
Ответ: x = 5, y = −2.

$\begin{equation*} \begin{cases} 4x - 7y = -12 &\\ -4x + 3y = 12 & \end{cases} \end{equation*}$
4x − 7y − 4x + 3y = −12 + 12
−4y = 0
y = 0
4x − 7 * 0 = −12
4x = −12
x = −3
Ответ: x = −3, y = 0.

$\begin{equation*} \begin{cases} 3x + 2y = 5 &\\ -5x + 2y = 45 & \end{cases} \end{equation*}$
3x + 2y − (−5x + 2y) = 5 − 45
3x + 2y + 5x − 2y = −40
8x = −40
x = −5
3 * (−5) + 2y = 5
−15 + 2y = 5
2y = 5 + 15
2y = 20
y = 10
Ответ: x = −5, y = 10.

$\begin{equation*} \begin{cases} 9x - 4y = -13 &\\ 9x - 2y = -20 & \end{cases} \end{equation*}$
9x − 4y − (9x − 2y) = −13 − (−20)
9x − 4y − 9x + 2y = −13 + 20
−2y = 7
y = −3,5
9x − 2 * (−3,5) = −20
9x = −20 − 7
9x = −27
x = −3
Ответ: x = −3, y = −3,5.