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CBSE Class 12 Math 2012 Solved Paper

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Question : 5 of 29
Marks: +1, -0
If a line has direction ratios 2,-1,-2 then what are its direction cosines?
Solution:  
The direction cosines are
222+(−1)2+(−2)2\frac{2}{\sqrt{2^2+(-1)^2+(-2)^2}} , −122+(−1)2+(−2)2\frac{-1}{\sqrt{2^2+(-1)^2+(-2)^2}} , −222+(−1)2+(−2)2\frac{-2}{\sqrt{2^2+(-1)^2+(-2)^2}}
= 23,−13,−23\frac{2}{3} , -\frac{1}{3} , -\frac{2}{3}
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