Find the direction cosines of a line which makes equal angles with the coordinate axes.

Let the direction cosines of the line making α with x-axis, β – with y axis and γ- with z axis are l, m and n

l = cos α, m = cos β and n = cos γ


Here given α = β = γ (line makes equal angles with the coordinate axes) ……….1


Direction Cosines are


l = cos α, m = cos β and n = cos γ


We have


l2 + m 2 + n2 = 1


cos2 α + cos2β + cos2γ = 1


From 1 we have


cos2 α + cos2 α + cos2 α = 1


3 cos2 α = 1



The direction cosines are



3