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Prove that three lines drawn from origin with direction cosines proportional to (1,-1,1),(2,-3,0),(1,0,3) lie on one plane .

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SOLUTION :Let `OVERSETTOA=i+j+koversettob=2i-3joversettoci+3k` The lines are co-planar if `oversettoa.(oversettobxxoversettoc)=0` Now `oversettoa.(oversettobxxoversettoc)=|(1,-1,1),(2,-3,0),(1,0,3):|=1(-9)+1(6)+1(3)=0`


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