Вправа 1121 алгебра Бевз гдз 7 клас

№ 1121 $$
\begin{aligned}
& \text { a) }\left\{\left.\begin{array}{l}
10 x-21 y=9, \\
5 x+14 y=29 ;
\end{array} \right\rvert\, \cdot(-2)\right. \\
& \left\{\begin{array}{c}
10 x-21 y=9 \\
-10 x-28 y=-58 ;
\end{array}\right. \\
& -49 y=-49
\end{aligned}
$$
–49y = –49
y = 1
5x + 14 • 1 = 29
5x = 29 – 14
5x = 15
x = 3
Відповідь: (3; 1) $$
\begin{aligned}
& \text { б) }\left\{\begin{array}{c}
8 x-3 y=2 \\
2 x+5 y=12 ; \mid \cdot(-4)
\end{array}\right. \\
& \left\{\begin{array}{c}
8 x-3 y=2 \\
-8 x-20 y=-48 ;
\end{array}\right.
\end{aligned}
$$
–23у = –46
у = 2
2х + 5 • 2 = 12
2х = 12 – 10
2х = 2
х = 1
Відповідь: (1; 2)