Q. 44.3( 30 Votes )
If a line makes angles 90°, 135°, 45° with x, y and z axes respectively, find its direction cosines.
Or
Find the vector equation of the line which passes through the point (3,4,5) and is parallel to the vector 
.
Answer :
Direction cosines of a line making angle α with x-axis, β with y-axis and γ with z-axis are l, m ,n.
l = cos α , m = cos β , n = cos γ
Here, α = 90° , β = 135° and γ = 45°
l = cos 90°
=0
m = cos 135°
= cos(180° - 45°)
n = cos 45°
OR
If the coordinates of a point A= (x1, y1, z1), then the position vector is
Hence, the position vector of point P = (3,4,5) is
If the position vector (
) of a point on the line and a vector (
) parallel to the line is given, then the vector equation of a line is given by
Here, 
and 
, then
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Find the vector and Cartesian equations of the line through the point (1, 2, -4) and perpendicular to the two lines.
and 
Write the vector equations of the following lines and hence determine the distance between them:
