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3D Geometry question

2025 · 3 Apr · Shift 2 · Q39
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3D Geometry question

2025 · 3 Apr · Shift 2 · Q39

JEE MainMathematics3D GeometryMCQ+4 / −1
The distance of the point (7,10,11)(7,10,11)(7,10,11) from the line x−41=y−40=z−23\frac{x-4}{1}=\frac{y-4}{0}=\frac{z-2}{3}1x−4​=0y−4​=3z−2​ along the line x−92=y−133=z−176\frac{x-9}{2}=\frac{y-13}{3}=\frac{z-17}{6}2x−9​=3y−13​=6z−17​ is
  1. A
    16
  2. B
    12
  3. C
    18
  4. D
    14
View written solutionFree

Correct answer: D

  1. Interpret the two lines

The given line from which distance is to be measured is x−41=y−40=z−23.\frac{x-4}{1}=\frac{y-4}{0}=\frac{z-2}{3}.1x−4​=0y−4​=3z−2​.

Since the direction ratios are (1,0,3)(1,0,3)(1,0,3), a parametric form is x=4+t,y=4,z=2+3t.x=4+t,\quad y=4,\quad z=2+3t.x=4+t,y=4,z=2+3t. So this line is L1:(4,4,2)+t(1,0,3).L_1:(4,4,2)+t(1,0,3).L1​:(4,4,2)+t(1,0,3).

The distance is to be measured along the line x−92=y−133=z−176.\frac{x-9}{2}=\frac{y-13}{3}=\frac{z-17}{6}.2x−9​=3y−13​=6z−17​. Its parametric form is x=9+2λ,y=13+3λ,z=17+6λ.x=9+2\lambda,\quad y=13+3\lambda,\quad z=17+6\lambda.x=9+2λ,y=13+3λ,z=17+6λ. So this line is L2:(9,13,17)+λ(2,3,6).L_2:(9,13,17)+\lambda(2,3,6).L2​:(9,13,17)+λ(2,3,6).

We are given the point P=(7,10,11).P=(7,10,11).P=(7,10,11).


  1. Meaning of “distance of the point from the line along the line”

We must pass a line through PPP parallel to L2L_2L2​, and find where it meets L1L_1L1​. The required distance is then the distance from PPP to that intersection point, measured along that line.

So the line through PPP parallel to L2L_2L2​ is x−72=y−103=z−116=μ.\frac{x-7}{2}=\frac{y-10}{3}=\frac{z-11}{6}=\mu.2x−7​=3y−10​=6z−11​=μ. Hence, x=7+2μ,y=10+3μ,z=11+6μ.x=7+2\mu,\quad y=10+3\mu,\quad z=11+6\mu.x=7+2μ,y=10+3μ,z=11+6μ.


  1. Find intersection of this line with L1L_1L1​

At intersection, coordinates satisfy both:

From L1L_1L1​: x=4+t,y=4,z=2+3t.x=4+t,\quad y=4,\quad z=2+3t.x=4+t,y=4,z=2+3t.

From the line through PPP: x=7+2μ,y=10+3μ,z=11+6μ.x=7+2\mu,\quad y=10+3\mu,\quad z=11+6\mu.x=7+2μ,y=10+3μ,z=11+6μ.

Equating coordinates:

4+t=7+2μ...(1)4+t=7+2\mu \quad ...(1)4+t=7+2μ...(1) 4=10+3μ...(2)4=10+3\mu \quad ...(2)4=10+3μ...(2) 2+3t=11+6μ...(3)2+3t=11+6\mu \quad ...(3)2+3t=11+6μ...(3)

From (2): 3μ=−6  ⟹  μ=−2.3\mu=-6\implies \mu=-2.3μ=−6⟹μ=−2.

Substitute into (1): 4+t=7+2(−2)=3  ⟹  t=−1.4+t=7+2(-2)=3 \implies t=-1.4+t=7+2(−2)=3⟹t=−1.

Check in (3): 2+3(−1)=2−3=−1,2+3(-1)=2-3=-1,2+3(−1)=2−3=−1, 11+6(−2)=11−12=−1,11+6(-2)=11-12=-1,11+6(−2)=11−12=−1, which matches, so intersection exists.

Thus the intersection point is obtained from the line through PPP at μ=−2\mu=-2μ=−2.


  1. Compute the required distance

Along the line through PPP, direction vector is d⃗=(2,3,6).\vec d=(2,3,6).d=(2,3,6). Its magnitude is ∣d⃗∣=22+32+62=4+9+36=49=7.|\vec d|=\sqrt{2^2+3^2+6^2}=\sqrt{4+9+36}=\sqrt{49}=7.∣d∣=22+32+62​=4+9+36​=49​=7.

Since the parameter value is μ=−2\mu=-2μ=−2, the distance from PPP to the intersection point is ∣μ∣ ∣d⃗∣=2×7=14.|\mu|\,|\vec d|=2\times 7=14.∣μ∣∣d∣=2×7=14.


  1. Conclusion

The required distance is 14.\boxed{14}.14​.

So the correct option is D.

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