Let A = (3, 4, 5), P = (–1, 2, 4)
B = (4, 6, 3) and Q = (1, 0, 5)
∴ Dr's of line AB are (4 – 3), (6 – 4), (3 – 5)= 1, 2, –2
and Dr's of line PQ are (1 + 1), (0 – 2), (5 – 4)= 2, –2, 1
∴ Dc's of line PQ =
,
−, =
,−, ∴ Projection of line segment AB on the line PQis
|(1)+(−)(2)+()(−2)| =