1.

Read the following passage and answer the questions. Consider the lines `L_(1):(x+1)/(3)=(y+2)/(1)=(z+1)/(2),L_(2):(x-2)/(1)=(y+2)/(2)=(z-3)/(3)` The unit vector perpendicualr to both `L_(1)` and `L_(2)` isA. `(-hati+7hatj+7hatk)/(sqrt(99))`B. `(-hati-7hatj+5hatk)/(5sqrt(3))`C. `(-hati+7hatj+5hatk)/(5sqrt(3))`D. `(7hati-7hatj-hatk)/(sqrt(99))`

Answer» Correct Answer - B
The equations of given lines in vector form may be written as `L_(1):vecr=(-hati-2hatj-hatk)+lambda(3hati+hatj+2hatk)`
and `" "L_(2):vecr=(2hati-2hatj+3hatk)+mu(hati+2hatj+3hatk)`
Since, the vector is perpendicular to both `L_(1)` and `L_(2).`
`|{:(hati,hatj, hatk),(3,1,2),(1,2,3):}|=-hati-7hatj+5hatk`
`:.` Required unit vector
`=((-hati-7hatj+5hatk))/(sqrt((-1)^(2)+(-7)^(2)+(5)^(2)))=(1)/(5sqrt(3))(-hati-7hatj+5hatk)`


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