1.

If l,m,n and l',m',n' be the direction cosines of two lines which include an angle theta, then

Answer»

`costheta=ll'+mm'+N n'`
`sintheta=ll'+mm'+n n'`
`costheta=mn'+m'n+nl'+n'l+lm'+l'm`
`sintheta=mn'+m'n+nl'+n'l+lm'+l'm`

ANSWER :A


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