Question

Решите систему уравнений
а) {3x+y=7
{9x-2y=1
В) {4x-y=10
{x=2y-1

Answer 1

а) {3х+у=7 |•2
{9х-2у=1

{6х+2у=14
{9х-2у=1

6х+9х=14+1

15х=15
х=1

3• 1+ у=7
у= 7-3
у=4

Answer 2

$\left \{ {{3x+y=7} \atop {9x-2y=1}} \right. \\\\ \left+ \{ {{6x+2y=14} \atop {9x-2y=1}} \right.$
_____________
15x = 15
x = 1
y = 7 - 3x = 7 - 3 * 1 = 7 - 3 = 4
Ответ : (1 ; 4)

$\left \{ {{4x-y=10} \atop {x=2y-1}} \right.\\\\ +\left \{ {{-8x+2y=-20} \atop {x-2y=-1}} \right.$
___________
- 7x = - 21
x = 3
y = 4x - 10 = 4 * 3 - 10 = 12 - 10 = 2
Ответ : (3 ; 2)