1
© NCERT
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THREE D IMENSIONAL G EOMETRY
465
Hence, from (1), the d c ’s of the line are
2
2
2
2
2
2
2
2
2
,
,
a
b
c
l
m
n
a
b
c
a
b
c
a
b
c
=±
= ±
= ±
+
+
+
+
+
+
where, depending on the desired sign of k, either a positive or a negative sign is to be
taken for l, m and n For any line, if a, b, c are direction ratios of a line, then ka, kb, kc; k ≠ 0 is also a
set of direction ratios