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Let $${{x - 2} \over 3} = {{y + 1} \over { - 2}} = {{z + 3} \over { - 1}}$$ lie on the plane $$px - qy + z = 5$$, for some p, q $$\in$$ R. The shortest distance of the plane from the origin is :

JEE · Math · previous-year question

  1. A.$$\sqrt {{3 \over {109}}} $$
  2. B.$$\sqrt {{5 \over {142}}} $$correct
  3. C.$${5 \over {\sqrt {71} }}$$
  4. D.$${1 \over {\sqrt {142} }}$$

Answer

B. $$\sqrt {{5 \over {142}}} $$

Explanation

$\frac{x-2}{3}=\frac{y+1}{-2}=\frac{z+3}{-1}=\lambda$ $(3 \lambda+2,-2 \lambda-1,-\lambda-3)$ lies on plane $p x-q y+z=5$ $p(3 \lambda+2)-q(-2 \lambda-1)+(-\lambda-3)=5$ $\lambda(3 p+2 q-1)+(2 p+q-8)=0$ $3 p+2 q-1=0\} p=15$ $2 p+q-8=0\} q=-22$ Equation of plane $15 x+22 y+z-5=0$ Shortest distance from origin $=\frac{|0+0+0-5|}{\sqrt{15^{2}+22^{2}+1}}$ $=\frac{5}{\sqrt{710}}$ $=\sqrt{\frac{5}{142}}$

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