1)
{2x +3y= 2
{-2x + 5y = - 18
2x + 3y - 2x + 5y = 2 + (-18)
8y = -16
y = -16/8
y = - 2
2x + 3*(-2) = 2
2x - 6 =2
2x = 2 + 6
2x = 8
x= 8/2
x = 4
ответ: (4 ; -2)
2)
{ x+ 4y = 39
{2x - y = 15 |*4
{x + 4y = 39
{8x - 4y = 60
x+4y +8x -4y = 39+60
9x = 99
x= 11
11 + 4y = 39
4y = 39 - 11
y = 28/4
y = 7
ответ: (11 ; 7)
№2.
1)
{7x+2y = 9
{5x + 2y = 11 |*(-1)
{7x +2y = 9
{ - 5x - 2y = -11
7x + 2y - 5x - 2y = 9 - 11
2x = -2
x = -1
7*(-1) + 2y = 9
2y = 9 +7
2y = 16
y = 8
ответ: (-1 ; 8)
2)
{ 9x - 2y =-17 |*(-1)
{ x - 2y = 7
{ - 9x + 2y = 17
{ x - 2y = 7
- 9x +2y +x - 2y = 17 + 7
-8x= 24
x = 24 / (-8)
x= 3
3 - 2y = 7
-2y = 7-3
-2y = 4
y = 4/(-2)
y = -2
ответ: (3 ; - 2)
3)
{x + 7y = 19
{ x + 5y = 13 | *(-1)
{ x +7y = 19
{ -x - 5y = -13
x + 7y - x - 5y = 19 - 13
2y = 6
y = 3
x + 7*3 = 19
x + 21 = 19
x = 19 - 21
x= -2
ответ : ( -2 ; 3).
4)
{5х - 2у = 15
{2x - y = 7 |*(-2)
{5x -2y =15
{ -4x +2y = -14
5x -2y -4x +2y = 15-14
x = 1
5*1 - 2y = 15
-2y = 15-5
-2y = 10
y = -5
ответ : ( 1 ; -5).