Prove that 1,1,1 cannot be direction cosines of a straight line.

Explanation

Here we have given,` l=1, m=1, n=1`

And, we know that-


`l^{2}+m^{2}+n^{2}=1`


Taking LHS,


`l^{2}+m^{2}+n^{2}=(1)^{2}+(1)^{2}+(1)^{2}`

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