InterviewSolution
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The direction cosines of the line `x-y+2z=5, 3x+y+z=6` areA. ` ( - 3 ) / ( 5 sqrt ( 2 ) ), ( 5 ) / ( 5sqrt2 ) , ( 4 ) / ( 5sqrt 2 ) `B. ` ( 3 ) /( 5sqrt 2 ) , ( - 5 ) /(5sqrt 2 ) , ( 4 ) / ( 5sqrt2 ) `C. ` ( 3 ) /( 5sqrt 2 ) , ( 5 ) / ( 5sqrt 2) , ( 4 ) / ( 5sqrt 2 ) `D. None of these |
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Answer» Correct Answer - A Vector normal to given planes are ` n_ 1 = hati - hatj + 2 hatk and n _ 2 = 3 hati + hatj + hatk ` . So , their line of intersection is parallel to the vector ` n = n _ 1 xx n _ 2 = |{:( hati , hatj , hatk ) , ( 1, -1, 2 ) , ( 3, 1 , 1 ) :}| = - 3 hati +5 hatj + 4hatk ` ` rArr hatn = ( - 3 ) / ( 5 sqrt 2 ) hati + ( 5 ) / ( 3 sqrt 2 ) hatj + ( 4 ) /( 5sqrt 2 ) hatk ` Hence, direction cosines of the line are ` ( - 3 ) / ( 5sqrt2 ) , ( 5 ) / ( 5sqrt2) , ( 4 ) / ( 5sqrt2 ) ` |
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