# 9.2 Gradient of Parallel Lines

9.2.1 Parallel Lines

1. Two straight lines are
parallel if they have
If PQ // RS,
then mPQ = mRS

2. If two straight lines have
they are parallel.
If mAB = mCD
then AB // CD
Example 1:
Determine whether the two straight lines are parallel.
(a) 2y – 4x = 6
y = 2x 5
(b) 2y = 3x 4
3y = 2x +12

Solution:
(a)
2y – 4x = 6
2y = 6 + 4x
= 2x + 3,   m1= 2
= 2x 5,   m2 = 2
m1= m2
Therefore, the two straight lines are parallel.

(b)