Which of the following lines has a slope of - 1/2?

x + 2y = 0

x - 2y = 0

-x + 2y = 0

y = x - 1/2

When we are looking for slope, let's use the slope intercept form ...

y = mx + b

this is where "m" is the slope and the "b" is the y-intercept ...

so, in your situation ... y = x = 1/2

The second line would have a slope of - 1/2 if you solve the equation for y