Вправи: 1198 (1-3)

1198. 1) Знайдіть розв’язок системи:

x + y = 7, y = 7 – x, y = 7 – x, y = 7 – x, y = 5,

2x + y = 9; 2x + 7 – x = 9; x + 7 = 9; x = 2; x = 2.

Відповідь: (2; 5);

2)

x – y = –2, x = y – 2, x = y – 2, x = y – 2, x = –7 –2, x = –9,

x – 2y = 5; y–2–2y=5; y–2y=5+2; y = –7; y = –7; y = –7.

Відповідь: (–9 ; –7 );

3)

y – x = 0, y = x, y = x, y = x, y = 3,

4x + y = 15; 4x + x = 15; 5x = 15; x = 3; x = 3.

Відповідь: (3; 3);

4)

5x + 2y = 2, 5x + 2y = 2, 5(2y + 10) + 2y = 2, 10y +50 +2y = 2,

x – 2y = 10; x = 2y + 10; x = 2y + 10; x = 2y + 10;

10y + 2y = 2 – 50, 12y = –48, y = –4, y = –4,

x = 2y + 10; x = 2y + 10; x = 2∙(–4) + 10; x = 2.

Відповідь: (2; –4);

5)

x – 3y = 7, x = 3y + 7, x = 3y + 7,

2x – 3y = –3; 2(3y + 7) – 3y = –3; 6y + 14 – 3y = –3;

x = 3y + 7, x = 3y + 7, x = 3y + 7, x = 3 ∙ (–173) + 7,

6y – 3y = –3 – 14; 3y = –17; y = –173; y = –173;

x = –10,

y = –173.

Відповідь: (–10; –173);

6)

5x – 3y = –19, 5x – 3y = –19, 5x – 3(–1–2x) = –19,

2x + y = –1; y = –1 –2x; y = –1 – 2x;

5x + 3 + 6x = –19, 11x = –22, x = –2, x = –2,

y = –1 – 2x; y = –1 – 2x; y = –1 –2 ∙ (–2); y = 3.

Відповідь: (–2 ; 3).