The shortest distance between the lines x−a+dα−δ=y−aα=z−a−dα+δ,x−b+cβ−γ=y−bβ=z−b−cβ+γ is

=a−d−b−ca−ba+d−b−cα−δαα+δβ−γββ+γC1→C1−C2,C3→C3−C2c−da−bd−c−δαδ−γβγ=0(∵C1 and C3 are identical)