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The shortest distance between the lines $${{x - 1} \over 0} = {{y + 1} \over { - 1}} = {z \over 1}$$ and x + y + z + 1 = 0, 2x – y + z + 3 = 0 is :

JEE · Math · previous-year question

  1. A.1
  2. B.$${1 \over 2}$$
  3. C.$${1 \over {\sqrt 2 }}$$
  4. D.$${1 \over {\sqrt 3 }}$$correct

Answer

D. $${1 \over {\sqrt 3 }}$$

Explanation

Plane through line of intersection is x + y + z + 1 + $$\lambda $$ (2x –y + z + 3) = 0 It should be parallel to given line $${{x - 1} \over 0} = {{y + 1} \over { - 1}} = {z \over 1}$$ $$ \therefore $$ 0(1 + 2$$\lambda $$) - 1(1 - $$\lambda $$) + 1(1 + $$\lambda $$) = 0 $$ \Rightarrow $$ $$\lambda $$ = 0 $$ \therefore $$ Required Plane : x + y + z + 1 = 0 Shortest distance of (1, –1, 0) from this plane = $${{\left| {1 - 1 + 0 + 1} \right|} \over {\sqrt {{1^2} + {1^2} + {1^2}} }}$$ = $${1 \over {\sqrt 3 }}$$

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