1. Выразите в каждой системе у через х: 1) {x - 3y = 5, 4x - 12y = 25; 2) {2x + 7y = 1, x - 3y = 2; 3) {3x - y = 4, 15x - 5y = 20; 4) {x = y - 3, 2x + y = 3; 5) {2y - x = 2, 4y - 2x = 3; 6) {y + 2x = 9, 3x - 5y = 4; 7) {3x + 2y = 7, 6x + 4y = 15; 8) {2x - 3y = -4, 6x - 9y = -12; 9) {x - 2y = 7, 3x + 2y = 5;

Выражаем y через x в каждой системе:

1)

• x - 3y = 5 => 3y = x - 5 => y = (x - 5)/3
• 4x - 12y = 25 => 12y = 4x - 25 => y = (4x - 25)/12

2)

• 2x + 7y = 1 => 7y = 1 - 2x => y = (1 - 2x)/7
• x - 3y = 2 => 3y = x - 2 => y = (x - 2)/3

3)

• 3x - y = 4 => y = 3x - 4
• 15x - 5y = 20 => 5y = 15x - 20 => y = (15x - 20)/5 = 3x - 4

4)

• x = y - 3 => y = x + 3
• 2x + y = 3 => y = 3 - 2x

5)

• 2y - x = 2 => 2y = x + 2 => y = (x + 2)/2
• 4y - 2x = 3 => 4y = 2x + 3 => y = (2x + 3)/4

6)

• y + 2x = 9 => y = 9 - 2x
• 3x - 5y = 4 => 5y = 3x - 4 => y = (3x - 4)/5

7)

• 3x + 2y = 7 => 2y = 7 - 3x => y = (7 - 3x)/2
• 6x + 4y = 15 => 4y = 15 - 6x => y = (15 - 6x)/4

8)

• 2x - 3y = -4 => 3y = 2x + 4 => y = (2x + 4)/3
• 6x - 9y = -12 => 9y = 6x + 12 => y = (6x + 12)/9 = (2x + 4)/3

9)

• x - 2y = 7 => 2y = x - 7 => y = (x - 7)/2
• 3x + 2y = 5 => 2y = 5 - 3x => y = (5 - 3x)/2