y=2x+13
y>0 would be a positive value
2x+13>0
subtract 13 from each side
2x >-13
divide by 2
x > -13/2
x > -6 1/2
y < 0 is a negative value
2x+13 < 0
2x<-13
x < -13/2
x < -6 1/2
if x > -6 1/2 it has a positive value
if x< -6 1/2 it has a negative value
x= -6 1/2 it equals 0