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A=1,2,3,B=5,0,6,C=0,4,1. If l,m,n be the direction cosines of the internal angular bisector ofBAC, then lmn=

a
28714
b
22714
c
38714
d
12714

detailed solution

Correct option is D

The vector along the internal angular bisector of a¯,b¯ isa¯a±b¯bHerea¯=AB¯ and b¯=AC¯It implies that a¯=6i−2j−3k and b¯=i+2j+2kHence, the vector along the internal angular bisector of  ∠BAC is a¯a+b¯b=25i+8j+5k21Therefore, the direction cosines are25714,8714,5714It implies that  l−m−n=12714

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