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The direction cosines of a line with direction ratios $(2, -1, 2)$ are:
A$(2/3, -1/3, 2/3)$, normalising by the magnitude $3$
B$(2, -1, 2)$, the direction ratios themselves as cosines
C$(1/3, -1/6, 1/3)$, halving the correct cosines on chart
D$(2/9, -1/9, 2/9)$, dividing by the squared magnitude here
Answer & Solution
Correct answer: A. $(2/3, -1/3, 2/3)$, normalising by the magnitude $3$
Magnitude $= \sqrt{4 + 1 + 4} = 3$; cosines = $(2/3, -1/3, 2/3)$.
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