5.5 Parallel Lines (Part 1)

5.5 Parallel Lines (Part 1)
 
(A) Gradient of parallel lines

1. Two straight lines are 
parallel if they have
the same gradient.
If PQ // RS,
then mPQ = mRS
   
2. If two straight lines have 
the same gradient, then  
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)
2y=3x4y=32x2,   m1=323y=2x+12y=23x+4,   m2=23m1m2