If and are direction cosines of the two lines inclined to each other at an angle then the direction cosines of the external bisector of the angle between the lines are 

a) 

b) 

c) 

d) 
If and are direction cosines of the two lines inclined to each other at an angle then the direction cosines of the external bisector of the angle between the lines are 

a) 

b) 

c) 

d) 
(c)
In Fig. is the external bisector
The coordinates of are
Therefore, direction ratios of are proportional to