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Explain solution RD Sharma Class 12 Chapter 26 Direction Cosines and Direction Ratios Exercise Very Short Answer Question, question 17 Maths.

Answers (1)

Answer:

\frac{2}{3},\frac{-1}{3},\frac{-2}{3}

Hint:

l=\frac{a}{\sqrt{a^{2}+b^{2}+c^{2}}}, \quad m=\frac{b}{\sqrt{a^{2}+b^{2}+c^{2}}}, \quad n=\frac{c}{\sqrt{a^{2}+b^{2}+c^{2}}}

 

Given:

D'R proportional to 2, -1, 2.

Solution:

Let l, m, n be direction cosine.

\begin{aligned} &l=\frac{2}{\sqrt{4+1+4}} \\ &m=\frac{-1}{\sqrt{4+1+4}} \\ &n=\frac{-2}{\sqrt{4+1+4}} \\ &l=\frac{2}{3} \\ &m=\frac{-1}{3} \\ &n=\frac{-2}{3} \\ &\langle l, m, n\rangle=\langle \frac{2}{3},\frac{-1}{3},\frac{-2}{3}\rangle \end{aligned}

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