If you solve all the equations for y, i.e. you write write all the lines in the form
[tex]y=mx[/tex]
then [tex]m[/tex] is the slope. So, you have
[tex]x-2y=0 \iff y=\dfrac{1}{2}x[/tex]
[tex]-x+2y=0 \iff y=\dfrac{1}{2}x[/tex]
[tex]x+2y=0 \iff y=-\dfrac{1}{2}x[/tex]
