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3D Geometry question

2025 · 24 Jan · Shift 1 · Q36
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  5. /2025 · 24 Jan · Shift 1 · Q36

3D Geometry question

2025 · 24 Jan · Shift 1 · Q36

JEE MainMathematics3D GeometryMCQ+4 / −1
Let the line passing through the points (−1,2,1)(-1,2,1)(−1,2,1) and parallel to the line x−12=y+13=z4\frac{x-1}{2}=\frac{y+1}{3}=\frac{z}{4}2x−1​=3y+1​=4z​ intersect the line x+23=y−32=z−41\frac{x+2}{3}=\frac{y-3}{2}=\frac{z-4}{1}3x+2​=2y−3​=1z−4​ at the point PPP. Then the distance of PPP from the point Q(4,−5,1)Q(4,-5,1)Q(4,−5,1) is
  1. A
    565 \sqrt{6}56​
  2. B
    555
  3. C
    555 \sqrt{5}55​
  4. D
    101010
View written solutionFree

Correct answer: C

  1. Write the required line through (−1,2,1)(-1,2,1)(−1,2,1)

    The line x−12=y+13=z4\frac{x-1}{2}=\frac{y+1}{3}=\frac{z}{4}2x−1​=3y+1​=4z​ has direction ratios (2,3,4)(2,3,4)(2,3,4).

    So the line passing through (−1,2,1)(-1,2,1)(−1,2,1) and parallel to it is x+12=y−23=z−14=λ\frac{x+1}{2}=\frac{y-2}{3}=\frac{z-1}{4}=\lambda2x+1​=3y−2​=4z−1​=λ

    Hence its parametric form is x=−1+2λ,y=2+3λ,z=1+4λ.x=-1+2\lambda,\quad y=2+3\lambda,\quad z=1+4\lambda.x=−1+2λ,y=2+3λ,z=1+4λ.

  2. Write the second line in parametric form

    Given x+23=y−32=z−41=μ\frac{x+2}{3}=\frac{y-3}{2}=\frac{z-4}{1}=\mu3x+2​=2y−3​=1z−4​=μ

    so x=−2+3μ,y=3+2μ,z=4+μ.x=-2+3\mu,\quad y=3+2\mu,\quad z=4+\mu.x=−2+3μ,y=3+2μ,z=4+μ.

  3. Find their point of intersection PPP

    At intersection, −1+2λ=−2+3μ...(1)-1+2\lambda=-2+3\mu \quad ...(1)−1+2λ=−2+3μ...(1) 2+3λ=3+2μ...(2)2+3\lambda=3+2\mu \quad ...(2)2+3λ=3+2μ...(2) 1+4λ=4+μ...(3)1+4\lambda=4+\mu \quad ...(3)1+4λ=4+μ...(3)

    From (1): 2λ−3μ=−12\lambda-3\mu=-12λ−3μ=−1

    From (2): 3λ−2μ=13\lambda-2\mu=13λ−2μ=1

    Solve these two equations:

    Multiply first by 333 and second by 222: 6λ−9μ=−36\lambda-9\mu=-36λ−9μ=−3 6λ−4μ=26\lambda-4\mu=26λ−4μ=2

    Subtract: 5μ=5⇒μ=15\mu=5 \Rightarrow \mu=15μ=5⇒μ=1

    Then from 3λ−2μ=13\lambda-2\mu=13λ−2μ=1: 3λ−2=1⇒3λ=3⇒λ=1.3\lambda-2=1 \Rightarrow 3\lambda=3 \Rightarrow \lambda=1.3λ−2=1⇒3λ=3⇒λ=1.

    Check in (3): 1+4(1)=5,4+1=51+4(1)=5,\quad 4+1=51+4(1)=5,4+1=5 so it is consistent.

    Therefore, P=(−1+2,  2+3,  1+4)=(1,5,5).P=(-1+2,\;2+3,\;1+4)=(1,5,5).P=(−1+2,2+3,1+4)=(1,5,5).

  4. Find distance from PPP to Q(4,−5,1)Q(4,-5,1)Q(4,−5,1)

    Using distance formula: PQ=(4−1)2+(−5−5)2+(1−5)2PQ=\sqrt{(4-1)^2+(-5-5)^2+(1-5)^2}PQ=(4−1)2+(−5−5)2+(1−5)2​ =32+(−10)2+(−4)2=\sqrt{3^2+(-10)^2+(-4)^2}=32+(−10)2+(−4)2​ =9+100+16=\sqrt{9+100+16}=9+100+16​ =125=55.=\sqrt{125}=5\sqrt{5}. =125​=55​.

  5. Match with options

    555\sqrt{5}55​ corresponds to Option C.

  6. Compare with stored correct answer

    Stored correct answer: C

    Our derived answer: C

    So they agree.

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