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JEE Advanced 2025 Paper 2 · Mathematics · Three Dimensional Geometry · medium

(x-1)/(2)=(y+1)/(3)=(z-2)/(1) and L2: x/1=(y-1)/(-1)=(z+2)/(2).

One or more options correct

Consider the lines L1: x−12=y+13=z−21L_1:\ \dfrac{x-1}{2}=\dfrac{y+1}{3}=\dfrac{z-2}{1} and L2: x1=y−1−1=z+22L_2:\ \dfrac{x}{1}=\dfrac{y-1}{-1}=\dfrac{z+2}{2}. Which of the following statements is(are) correct?
  1. A. L1L_1 and L2L_2 intersect
  2. B. The shortest distance between L1L_1 and L2L_2 is 783\dfrac{7}{\sqrt{83}}
  3. C. The shortest distance between L1L_1 and L2L_2 is 759\dfrac{7}{\sqrt{59}}
  4. D. The plane containing L1L_1 and parallel to L2L_2 is 7x−3y−5z=77x-3y-5z=7
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Answer: B

Direction vectors d⃗1=(2,3,1)\vec d_1=(2,3,1), d⃗2=(1,−1,2)\vec d_2=(1,-1,2); d⃗1×d⃗2=(7,−3,−5)\vec d_1\times\vec d_2=(7,-3,-5), magnitude 83\sqrt{83}. Points (1,−1,2)∈L1(1,-1,2)\in L_1 and (0,1,−2)∈L2(0,1,-2)\in L_2; their difference is (−1,2,−4)(-1,2,-4) with dot product −7−6+20=7-7-6+20=7 with the normal. So the shortest distance is 7/83≠07/\sqrt{83}\ne0, lines are skew. (A) False: the distance is non-zero. (B) True. (C) False: 59\sqrt{59} is wrong magnitude. (D) False: the plane through (1,−1,2)(1,-1,2) with normal (7,−3,−5)(7,-3,-5) is 7x−3y−5z=7+3−10=07x-3y-5z=7+3-10=0, i.e. 7x−3y−5z=07x-3y-5z=0; the constant 77 belongs to the plane containing L2L_2.
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