Correct Answer - A
Vectors normal to given planes are `vecn_(1)=hati-hatj+2hatk` and `vecn_(2)=3hati+hatj+hatk`.
So their line of intersection is parallel to the vector
`vecn=vecn_(1)xxvecn_(2)=|(hati,hatj,hatk),(1,-1,2),(3,1,1)|=-3hati+5hatj+4hatk`
`impliesvecn=(-3)/(5sqrt(2))hati+5/(5sqrt(2))hatj+4/(5sqrt(2))hatk`
Hence, direction cosines of the line are `(-3)/(5sqrt(2)),5/(5sqrt(2)),4/(5sqrt(2))`
