As 2x + y = -1
Then,
y = - 1 - 2x
We can to replace on the bellow equation.
x + 2y = 4
x + 2.( -1 -2x) = 4
Doing the distributive
x + 2.(-1) + 2.(-2x) = 4
x -2 -4x = 4
-3x -2 = 4
-3x = 4 + 2
-3x = 6
x = 6/-3
x = -2
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Then, the value of y will be:
y = -1 -2x
y = -1 -2.(-2)
y = -1 + 4
y = 3
