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Need solution for RD Sharma maths class 12 chapter 26 Direction Cosines and Direction Ratios exercise Fill in the blanks question 15

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Final Answer:  \frac{\sqrt{23}}{6}

Hint:

Use the property of direction cosine

Given:

Direction cosine   =\left(\frac{1}{2}, \frac{1}{3}, n\right)

To Find: 

Value of n

Solution:

By property of direction cosine, we get

\begin{aligned} &l^{2}+m^{2}+n^{2}=1 \\\\ &\left(\frac{1}{2}\right)^{2}+\left(\frac{1}{3}\right)^{2}+n^{2}=1 \\\\ &\frac{1}{4}+\frac{1}{9}+n^{2}=1 \end{aligned}

\begin{aligned} &n^{2}=1-\frac{1}{4}-\frac{1}{9} \\ &n^{2}=\frac{23}{36} \\\\ &n=\sqrt{\frac{23}{36}} \\\\ &n=\frac{\sqrt{23}}{6} \end{aligned}
 

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