alleryThe direction cosines of a line whose direction ratios are $2,-1,2$ are:
A$2, -1, 2$
B$\tfrac12, -\tfrac11, \tfrac12$
C$\tfrac29, -\tfrac19, \tfrac29$
D$\tfrac23, -\tfrac13, \tfrac23$
Answer & Solution
Correct answer: D. $\tfrac23, -\tfrac13, \tfrac23$
Divide by √(2²+1²+2²)=3: direction cosines are (2/3, −1/3, 2/3).
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