$\begin{equation*} \begin{cases} 25x - 18y = 75 &\\ 5x - 4y = 5 |*5 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 25x - 18y = 75 &\\ 25x - 20y = 25 & \end{cases} \end{equation*}$
25x − 18y − (25x − 20y) = 75 − 25
25x − 18y − 25x + 20y = 50
2y = 50
y = 25
5x − 4 * 25 = 5
5x − 100 = 5
5x = 5 + 100
5x = 105
x = 21
Ответ: x = 21, y = 25.

$\begin{equation*} \begin{cases} 35x = 3y + 5 |*4 &\\ 49x = 4y + 9 |*3 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 140x = 12y + 20 &\\ 147x = 12y + 27 & \end{cases} \end{equation*}$
140x − 147x = 12y + 20 − (12y + 27)
−7x = 12y + 20 − 12y − 27
−7x = −7
x = 1
35 * 1 = 3y + 5
3y = 35 − 5
3y = 30
y = 10
Ответ: x = 1, y = 10.

$\begin{equation*} \begin{cases} 8y - 5z = 23 |*2 &\\ 3y - 2z = 6 |*5 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 16y - 10z = 46 &\\ 15y - 10z = 30 & \end{cases} \end{equation*}$
16y − 10z − (15y − 10z) = 46 − 30
16y − 10z − 15y + 10z = 16
y = 16
3y − 2z = 6
3 * 16 − 2z = 6
48 − 2z = 6
2z = 48 − 6
2z = 42
z = 21
Ответ: y = 16, z = 21.

$\begin{equation*} \begin{cases} 13x - 15y = -48 &\\ 2x + y = 29 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 13x - 15y = -48 &\\ 2x + y = 29 |*15 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 13x - 15y = -48 &\\ 30x + 15y = 435 & \end{cases} \end{equation*}$
13x − 15y + 30x + 15y = −48 + 435
43x = 387
x = 9
2 * 9 + y = 29
18 + y = 29
y = 29 − 18
y = 11
Ответ: x = 9, y = 11.

$\begin{equation*} \begin{cases} 7x + 4y = 74 &\\ 3x + 2y = 32 |*2 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 7x + 4y = 74 &\\ 6x + 4y = 64 & \end{cases} \end{equation*}$
7x + 4y − (6x + 4y) = 74 − 64
7x + 4y − 6x − 4y = 10
x = 10
3x + 2y = 32
3 * 10 + 2y = 32
30 + 2y = 32
2y = 32 − 30
2y = 2
y = 1
Ответ: x = 10, y = 1.

$\begin{equation*} \begin{cases} 11u + 15v = 1,9 &\\ -3u + 5v = 1,3 |*3 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 11u + 15v = 1,9 &\\ -9u + 15v = 3,9 & \end{cases} \end{equation*}$
11u + 15v − (−9u + 15v) = 1,9 − 3,9
11u + 15v + 9u − 15v = −2
20u = −2
u = −0,1
−3 * (−0,1) + 5v = 1,3
0,3 + 5v = 1,3
5v = 1,3 − 0,3
5v = 1
v = 0,2
Ответ: u = −0,1, v = 0,2.