The square of the projection of the join of the points 1,4,7 and 2,5,8 on the line whose direction cosines are13,13,13, is

The length of the projection of the line segment joining Ax1,y1,z1,Bx2,y2,z2  on the line whose direction cosines are l,m,n is lx2−x1+my2−y1+nz2−z1Hence, the  projection of the join of the points 1,4,7and 2,5,8on the linewhose direction cosines are13,13,13 is131+1+1=3 Therefore, the required value is 3