If a line makes angles 90° and 60° respectively with the positive directions of x and y axes, find the angle which it makes with the positive direction of the z-axis.
suppose the direction cosines of the line be l,m,and n.
we know that l2 + m2+n2 = 1
Let the line make angle θ with the positive direction of the z-axis.
α = 90°, β = 60° γ = θ
Thus,
cos2 90 + cos260 + cos2θ =1