ax + by - p = 0....(1)
cx + dy - q = 0....(2)
from the equations we get a1 = a, a2 = c, b1 = b, b2 = d, c1 = -p, c2 = -q
so a1/a2 = a/c
b1/b2 = b/d
c1/c2 = -p/-q or p/q
Equating the following
a/c = b/d
by cross multiplication
ad = bc
but in question it is given ad is not equal to bc
so a1/a2 is not equal to b1/b2
so it is a unique solution