Question

Pls help!!!

in which line is a mistake first made when solving the following system of equations by substitution? 2x - y =-4 3x + y = -9

line 1: 2x -y = -4
y= 3x-9
line 2: 2x-(3x-9)=-4
line 3: 2x-3x+9=-4
line 4: -1x + 9 = -4
line 5: -1x = -13
line 6: x = 13

Answer 1

The very first line has an error.

Explanation:

When you are solving the second system of equations for y, you need to subtract 3x from both sides and therefore it should be negative.

3x + y = -9

y = -3x - 9

Since the 3x isn't negative in the first line, there is an error.