Gradient of PB (m1) = m
Gradient of PB’ (m2) =  1
m
If the gradients of the two perpendicular lines
are m1 and m2, then m1m2 = -1.

If two lines are parallel with one another, the
gradient of the two lines are the same.
m1
m2
m1 = m2
1)
Find the equation of the line that is parallel to
6x + 2y = 5 and passing through point (4,8).
2 y  6 x  5
5
y  3 x 
2
y  8  3( x  4)
y  3 x  4
2)
Find the equation of the line that is perpendicular
to y = 3x + 5 and passing through point (-2,5).
1
m2  
3
1
y  5   ( x  2)
3
3 y  15   x  2
3 y   x  13