$\begin{equation*} \begin{cases} 40x + 3y = -10 &\\ 20x - 7y = -5 | *(-2) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 40x + 3y = -10 &\\ -40x + 14y = 10 & \end{cases} \end{equation*}$
40x + 3y − 40x + 14y = −10 + 10
17y = 0
y = 0
20x − 7y = −5
20x = −5 + 7y
20x = −5 + 7 * 0
20x = −5
x = −5 : 20
x = −0,25
Ответ: (−0,25;0)

$\begin{equation*} \begin{cases} 5x + 2y = 1 | *(-3) &\\ 15x + 3y = 3 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} -15x - 6y = -3 &\\ 15x + 3y = 3 & \end{cases} \end{equation*}$
−15x − 6y + 15x + 3y = −3 + 3
−3y = 0
y = 0
5x + 2y = 1
5x = 1 − 2y
5x = 1 − 2 * 0
5x = 1
x = 0,2
Ответ: (0,2;0)

$\begin{equation*} \begin{cases} 3x + 8y = 13 | *2 &\\ 5x - 16y = 7 & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 6x + 16y = 26 &\\ 5x - 16y = 7 & \end{cases} \end{equation*}$
6x + 16y + 5x − 16y = 26 + 7
11x = 33
x = 33 : 11
x = 3
3x + 8y = 13
8y = 13 − 3x
8y = 13 − 3 * 3
8y = 13 − 9
8y = 4
y = 4 : 8
y = 0,5
3x + 8y = 13
3x = 13 − 8y
3x = 13 − 8 * 0,5
3x = 13 − 4
3x = 9
x = 9 : 3
x = 3
Ответ: (3;0,5)

$\begin{equation*} \begin{cases} 10x + 15y = -45 &\\ 2x - 3y = 33 | *(-5) & \end{cases} \end{equation*}$
$\begin{equation*} \begin{cases} 10x + 15y = -45 &\\ -10x + 15y = -165 & \end{cases} \end{equation*}$
10x + 15y − 10x + 15y = −45 − 165
30y = −210
y = −210 : 30
y = −7
2x − 3y = 33
2x = 33 + 3y
2x = 33 + 3 * (−7)
2x = 33 − 21
2x = 12
x = 12 : 2
x = 6
Ответ: (6;−7)