3 (a)) Fig 11 3
r
Z
X
Y
R
S
P ( , , )
x y z
A
Oα
A
O
P
x
α
α
Fig 11 2
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 MATHEMATI CS
466
Let l, m, n be the direction cosines of the line PQ and let it makes angles α, β and  γ
with the x, y and z-axis, respectively