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  • Provide solution for RD Sharma Maths Class 12 Chapter 26 Directions Cosines and Direction Ratios Exercise Multiple Choice Question, question 17.

Provide solution for RD Sharma Maths Class 12 Chapter 26 Directions Cosines and Direction Ratios Exercise Multiple Choice Question, question 17.

Answers (1)

Final Answer:

(d) k =\frac{1}{\sqrt{3}} \text{or}\frac{-1}{\sqrt{3}}

Hint: Use property of direction cosines

l^2+m^2+n^2=1

Given: Direction cosine of line are k,k,k

To Find: value of k

Solution: Since direction cosine of line are k,k,k

\therefore l=k,m=k \; \; \&\; \; n=k

We know that

\begin{aligned} &l^{2}+m^{2}+n^{2}=1 \\ &k^{2}+k^{2}+k^{2}=1 \\ &3 k^{2}=1 \\ &k=\pm \frac{1}{\sqrt{3}} \end{aligned}

Therefore, option (d) is correct

i.e. k=\pm \frac{1}{\sqrt{3}}

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