1)
{x-y=2 ⇒ x= 2+y
{2x-3y = -1
2*(2+y) -3y = -1
4 +2y -3y =-1
-y = -1 -4
-y = -5
y = 5
x= 2 + 5
x=7
ответ: (7;5)
2)
{-x+y =4 ⇒ y = 4+x
{4x+y = -1
4x +4+x = -1
5x = -1-4
5x= -5
x=-1
y= 4 + (-1)
y= 3
ответ: (-1 ;3)
3)
{3x+y =4 ⇒ y= 4-3x
{5x+y =10
5x + 4-3x = 10
2x+4=10
2x=10-4
2x=6
x=6/2
x=3
y= 4 - 3*3
y= 4 - 9
y = - 5
ответ: (3 ; -5)
4)
{8x-3y =7
{3x+y = 9 ⇒ y = 9-3x
8x -3*(9-3x) = 7
8x - 27 + 9x = 7
17x = 7+27
17x= 34
x= 34/17
x=2
y= 9 - 3*2
y = 9-6
y=3
ответ: (2 ;3)
5)
{x+5y = -2 ⇒ x= -2 - 5y
{0.5x-y=6
0.5 *(-2 - 5y) - y = 6
-1 - 2.5y - y = 6
-3.5y = 6+1
-3.5y = 7
y= 7 /(-3.5)
y= -2
x =-2 - 5 *(-2)
x= -2 + 10
x= 8
ответ: ( 8 ; -2)
6)
{ 12x - y = 18 ⇒ -y = 18-12x ⇒ y = 12x-18
{ x + 0.5y = 5
x + 0.5*(12x - 18) = 5
x + 6x - 9 = 5
7x = 5 +9
7x = 14
x = 14/7
x= 2
y = 12*2 - 18
y=24 - 18
y = 6
ответ : (2;6)