Will someone please help me understand? I don't know why I got the answer wrong.

You need to rewrite the given equations in standard form y = mx +b, where m is the slope.
First equation:
x + 2y = 0
Subtract x from each side:
2y = -x + 0
Divide both sides by 2:
y = -x/2 +0 = y = -1/2x +0
This give you a negative 1/2 slope
The first equation is the correct one.
Answer:
x + 2y = 0.
Step-by-step explanation:
Let's see what slope we get with the answer you gave:
- x + 2y = 0
Convert to slope/intercept form ( y = mx + c).
- x + x + 2y = 0 + x ( adding x to both sides of the equation).
2y = x
Divide both sides by 2:
y = 1/2 x
That is the slope is 1/2.
Correct is x + 2y = 0:
2y = -x
y = -1/2 x