d1 = ax + by + c = 0 and d2= mx + ky + f = 0
if they are parallel :
[tex]\frac{a}{m} = \frac{b}{k} \neq \frac{c}{f}[/tex]
8x + 2y = 7
8x + 2y - 7 = 0
- 8x + 2y -9 = 0
- 4x + y -6 = 0
- 16x + 4y - 19 = 0
you can create more whatever you want =)
Hope this helps ^-^
