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Prove that 1,1,1 cannot be direction cosines of a straight line. |
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Answer» Sum of squares of direction cosines of a straight line is always `1`. Here, sum of squares of direction cosines ` = 1^2+1^2+1^2 = 3 ` As `3 !=1`, so `(1,1,1)` can not be direction cosines of a straight line. |
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