Class 12 | 3D Geometry | If l 1 , m 1 , n 1 , l 2 , m 2 , n 2 a n d l 3 , m 3 , n 3 are the direction cosines of three mutually perpendicular lines,then prove that the line whose direction cosines are proportional to l 1 + l 2 + l 3 , m 1 + m 2 + m 3 a n d n 1 + n 2 + n 3 makes equal angles with them.