 If cos α, cos β and cos γ are the direction cosines of a line then cos^{2} α + cos^{2} β + cos^{2} γ = 1
 If cos α, cos β and cos γ are the direction cosines of a line passing through the point (a,b,c) then
(x  a)/cos α = (y  b)/cos β = (z  c)/cos γ is the equation of the line.
 If (x_{1}, y_{1}, z_{1}) and (x_{2}, y_{2}, z_{2}) are two points through which a line pass then
(x  x_{1})/(x_{2}  x_{1}) = (y  y_{1})/(y_{2}  y_{1}) = (z  z_{1})/(z_{2}  z_{1}) is the equation of the line.
