Find the projection of the line segment joining the points (1, 2, 3), (4, 3, 1) on the line with direction ratios 3, –6, –2.
A directed line segment makes angles 45° and 60° with x-axis and y-axis and an acute angle with z-axis. If P (– 1, 2, – 3) and Q (4, 3, 1) are two points in space, find the projection of PQ on the given line.
If P, Q, R, S are the points (– 2, 3, 4), (– 4, 4, 6), (4, 3, 5), (0, 1, 2), prove by projection that PQ is perpendicular to RS.
Let l, m, n be the direction-cosines of the line and let the length of the line segment be r.
∵ projections of the line segment on the axis are 12, 4, 3,
∴ l r = 12, m r = 4, n r = 3
Squaring and adding, we get,
(l2 + m2 + n2) r2 = 144 + 16 + 9
∴ (1) (r)2 = 169, ∴ r = 13
∴ length of the line = 13 units
and direction-cosines of line are
The projections of a directed line segment on the co-ordinate axes are 6, -3, 2. Find its length and direction cosines.