the position o the vectors A,B,C of a triangle are i-j-3k, 2i+j-2k and -5i+2j-6k respectively.the length of the bisector AD of the angle BAC where D is on the line segment BC,is

1-15/2 2-¼ 3-11/2 4-none

see as AD is internal bisector o angle BAC , it ( that is the point D ) will divide  BD and DC in the ratio of AB/AC i.e 1:3 . now using the division formula get the cordinate of D . and find the magnitude of AD.. and    i am getting the answer (3/4)*10^1/2  . i.e none of these

if this is not the answer then please post the solution .. 

 

 

 but   think this is a correct approach