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)/2^1/2