The direction cosines of two lines are connected by the relations 1+m−n=0 1 + m - n = 0 1+m−n=0 and lm−2mn+nl=0 lm - 2mn + nl = 0 lm−2mn+nl=0. If θ \theta θ is the acute angle between those lines, then cosθ= \cos \theta = cosθ= ?