If a, b, c are three mutually perpendicular vectors, then the projection of the vector [l a/|a| + m b/|b| + n (a+b)/|a+b|] along the angular bisector of vectors a and b may be given as a) (l2 + m2)/(l2+m2+n2)1/2 b) (l2+m2+n2)1/2 c) (l2+m2)1/2/(l2+m2+n2)1/2 d) (l+m)/21/2

Is there any information given in addition like about l,m,n etc

is the answer c

no