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Explain solution RD Sharma Class 12 Chapter 26 Direction Cosines and Direction Ratios Exercise Very Short Answer Question, question 11 Maths.

Answers (1)

Answer:

\frac{3\pi}{4}

Hint:

Cosine is trigonometric ratio

Given:

Distance ratio (0, -1, -1)

Solution:

here,  a=0,  b=1,  c= -1

let direction cosine are l, m, n

\begin{aligned} &l=\frac{a}{\sqrt{a^{2}+b^{2}+c^{2}}} \\ &m=\frac{b}{\sqrt{a^{2}+b^{2}+c^{2}}} \\ &n=\frac{c}{\sqrt{a^{2}+b^{2}+c^{2}}} \end{aligned}

\begin{aligned} &\cos \theta=n=\frac{(-1)}{\sqrt{(0)^{2}+(1)^{2}+(-1)^{2}}} \\ &\cos \theta=-\frac{1}{\sqrt{2}} \\ &\theta=\frac{3 \pi}{4} \end{aligned}

 

 

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