why do we find only direction cosines of a line in space and not direction sines?
supposing a line makes angle "x" with x- axis
projection of it ..i.e. cosine of tht line is taken as "lcos(x)" (l-> is length of vector)
where if we have to getthe sine component of this vector .......then a line perpendicular to x-axis is to be taken .....for us to write "lsin(x)"
but in 3D-geo......we have 2 lines perp to x-axis ...y and z axis
so determining sines of the lines is difficult.....the same is the reason why we dont have direction sines
hope i am right