Question

A)5x+y=-1
13x+4y=13
D)2x-5=y-4
7x-y=y+3
C)2x-5=y-4
7x-y=y+3​

Answer 1

A)

{5x+y=-1      . ( -4)

{13x+4y=13

{-20x -4y = 4

{13x+4y=13

______________

-7x = 17

x = - 17/7

______________

13x + 4y = 13

13 (-17/7) + 4y = 13

-221/7 + 4y = 13

4y = 13 + 221/7

4y = 312/7

y = 312/7 . 1/4

y = 312/28

y = 78/7

D)

{2x-5=y-4

{7x-y=y+3 -> 7x -y + y = 3 -> 7x = 3 -> x = 3/7

x = 3/7

___________________________

2x - 5 = y - 4

2 (3/7) - 5 + 4 = y

y = 6/7 - 1

y = -1/7

C)

{2x-5=y-4 -> 2x - y = -4 + 5 -> 2x -y = 1

{7x-y=y+3​ -> 7x -y -y = 3 -> 7x -2y = 3

{2x -y = 1 . (-2)

{7x -2y = 3

____________

{-4x + 2y = -2

{7x -2y = 3

__________________

3x = 1

x = 1/3

7x - 2y = 3

7 (1/3) - 2y = 3

2y = 7/3 -3

2y = -2/3

y = -2/3 . 1/2

y = -2/6

y = -1/3