Class 12

Math

3D Geometry

Three Dimensional Geometry

What are the direction cosines of the y-axis?

If $α,β,$ and $γ$ are the angles made by the line segment with the coordinate axis.

$cosα,cosβ$ and $cosγ$ are called as the direction cosines and are usually denoted by $l,m$ and $n.$

$l=cosα,m=cosβ$ and $n=cosγ$

Clearly the y-axis makes an angle of $90_{o},0_{o},90_{o}$ ie., with the x-axis, y-axis, z-axis respectively

so its direction cosines are $cos90_{o},cos0_{o},cos90_{o}$ ie., $0,1,0$