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 of∠BAC, then l−m−n=

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