Question

what is the solution of the system? Use substitution.
3x-y=-9
4x -y=-4
my answer is (-5,-6)
can you please help

Answer 1

well, did you try your solution to see whether it works?

3(-5)-(-6) = -15+6 = -9
4(-5)-(-6) = -20+6 = -14

Clearly not. SO, what happened? Using the first equation, we see that

y = 3x+9

Using that in the other equation, we get

4x-(3x+9) = -4
4x-3x-9 = -4
x = 5
So, y = 3x+9 = 15+9 = 24

Now if we check, we get

3*5-24 = 15-24 = -9
4*5-24 = 20-24 = -4

Better check your work to see where you went astray. Too bad you didn't see fit to show us your work, so now the rest of it is up to you.