Equation A: 2x + y = -5 ⇒ y = -2x - 5
Equation B: 2x + 3y = 9
2x + 3 (-2x - 5) = 9
2x - 6x - 15 = 9
-4x = 9 + 15
-4x/4 = 24/-4
x = -6
Substitute -6 for x in any of the two equations:
2x + y = -5
2 (-6) + y = -5
-12 + y = -5
y = -5 + 12
y = 7
The solution is (-6, 7)
To check:
2(-6) + 7 = -5
-12 + 7 = -5
-5 = -5
2x + 3y = 9
2(-6) + 3 (7) = 9
-12 + 21 = 9
9 = 9
