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Explain solution RD Sharma class 12 Chapter 27 Striaght Line in Space Exercise Fill in the blanks question 4

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Answer :    \pm \frac{1}{\sqrt{3}}

Hint :    l^{2}+m^{2}+n^{2}=1   

Given  :   l,l,l   are direction cosine of a line ,

Solution  : Since , direction cosine  of a line are  l,l\; \text{and} \: l

                  \therefore l=l, \mathrm{~m}=l \text { and } \mathrm{n}=l

                     We know that  , l^{2}+m^{2}+n^{2}=1

                   \begin{aligned} &=>l^{2}+l^{2}+l^{2}=1 \\ & \end{aligned}

                   \Rightarrow>l^{2}=\frac{1}{3} \\

                 \therefore l=\pm \frac{1}{\sqrt{3}}

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