1)
{y = 2x
{2x + 5y = 24
Метод подстановки.
2x + 5*2x = 24
2x + 10x = 24
12x = 24
x = 24 : 12
x=2
y = 2*2
y= 4
ответ : (2 ; 4 ) .
2)
{2х - у = 3 ⇒ y = 2x - 3
{7x + 3y = 4
7x + 3*(2x -3) = 4
7x + 6x - 9 = 4
13x = 4+9
13x = 13
x=1
y =2*1 - 3 = 2-3
y = -1
ответ: (1 ; - 1) .
3)
{x -5y =11 ⇒ x = 11 +5y
{3x - 5y = 13
3(11+5y) - 5y = 13
33 + 15y - 5y = 13
10y = 13 - 33
10y = -20
y = -20 :10
у= -2
х = 11 + 5*(-2) = 11 +(-10)
х = 1
ответ: (1 ; -2) .