you have in the first equation "+y" and in the second "-y" So, you add the 2 equations, so we can remove this 2 letters since they're opposite numbers. So, we get: -4x + y -5x - y = 21 + 6 -4x -5x = 21 + 6
Then, you add -4x -5x = 21 + 6 -9x = 27
Then, you move the -9 to the other part, next to the 27. And since it was a multiplication, it becomes a division. x = [tex] -\frac{27}{9} [/tex] [tex]x = -3[/tex]
Then, you choose an equation of the system, and you replace x by it's value so you can find y. I'll take the first equation.
-4x + y = 6 -4*-3 + y = 6 12 + y = 6
Then, you move 12 to the other part next to the 6. And since it was a positive number, it becomes a negative number. So y = 6 - 12 y = -6
So, the solution of the proposed system is (x;y) = (6;-6) x = 6 y = -6
