Question

{2x + 7y = 2 {x + y = -1

Answer 1

1st equation: 2x + 7y = 2
2nd equation: x + y = -1

find x using the 2nd equation:
x + y = -1
x = -y - 1

Substitute x by its value in the 1st equation to find the value of y.
2x + 7y = 2
2(-y-1) + 7y = 2
-2y -2 + 7y = 2
-2y + 7y =2 + 2
5y = 4
y = 4/5

Substitute the value of y in the value of x formula
x = -y -1
x = -4/5 - 1
x = -4/5 - (1*5/5)  *to have the same denominator
x = -4/5 - 5/5
x = (-4-5)/5
x = -9/5

To check: x = -9/5 ; y = 4/5

x + y = -1
-9/5 + 4/5 = -9+4/5 = -5/5 = -1

2 (-9/5) + 7(4/5) = 2
-18/5 + 28/5 = -18+28/5 = 10/5 = 2