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Question: Answered & Verified by Expert
If the length of a vector be 21 and direction ratios be $2,-3,6$ then its direction cosines are
MathematicsThree Dimensional GeometryJEE Main
Options:
  • A $\frac{2}{21}, \frac{-1}{7}, \frac{2}{7}$
  • B $\frac{2}{7}, \frac{-3}{7}, \frac{6}{7}$
  • C $\frac{2}{7}, \frac{3}{7}, \frac{6}{7}$
  • D None of these
Solution:
1643 Upvotes Verified Answer
The correct answer is: $\frac{2}{7}, \frac{-3}{7}, \frac{6}{7}$
D.c.'s are $\frac{2}{\sqrt{2^2+(-3)^2+6^2}}, \frac{-3}{\sqrt{49}}$ and $\frac{6}{\sqrt{49}}$ or $\frac{2}{7}, \frac{-3}{7}, \frac{6}{7}$

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