Задание 1
{3x + y = 11,
{3x – y = 1.
6x = 12;
x = 12 ÷ 6 = 2.
Если x = 2, то
3 × 2 – y = 1;
6 – y = 1;
–y = 1 – 6 = –5;
y = 5.
Ответ: (2; 5).
Задание 2
{y – 2x = 1,
{6x + y = 9.
{y = 1 + 2x,
{6x + y = 9.
6x + 1 + 2x = 9;
8x + 1 = 9;
8x = 9 – 1 = 8;
x = 1.
Если x = 1, то y = 1 + 2 × 1 = 1 + 2 = 3.
Ответ: (1; 3).
Задание 3
{2x – 3y = –9,
{3x – y = 4.
{2x – 3y = –9,
{y = –4 + 3x.
2x – 3(–4 + 3x) = –9;
2x + 12 – 9x = –9;
–7x + 12 = –9;
–7x = –9 – 12 = –21;
x = 3.
Если x = 3, то y = –4 + 3 × 3 = –4 + 9 = 5.
Ответ: (3; 5).
Задание 4
{4x + y = 0,
{x + 2y = –7.
{y = –4x,
{x + 2y = –7.
x + 2 × (–4x) = –7;
x – 2 × 4x = –7;
x – 8x = –7;
–7x = –7;
x = 1.
Если x = 1, то y = –4 × 1 = –4.
Ответ: (1; –4).