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QJEEM23Ma81f7: JEE Main 2023 Mathematics - Class 12 JEEM23Ma81f7 Solution: Let be the set of all values of , for which the shortest…

Let S\mathrm{S} be the set of all values of λ\lambda , for which the shortest distance between

the lines x−λ0=y−34=z+61\frac{x-\lambda}{0}=\frac{y-3}{4}=\frac{z+6}{1} and x+λ3=y−4=z−60\frac{x+\lambda}{3}=\frac{y}{-4}=\frac{z-6}{0} is 13. Then 8∣∑λ∈Sλ∣8\left|\sum\limits_{\lambda \in S} \lambda\right| is equal to :

Multiple Choice Options

  • A 306
  • B 304
  • C 308
  • D 302

Step-by-Step Verified Solution

Given the two lines :

x−λ0=y−34=z+61x+λ3=y−4=z−60\frac{x-\lambda}{0}=\frac{y-3}{4}=\frac{z+6}{1} \\\\\frac{x+\lambda}{3}=\frac{y}{-4}=\frac{z-6}{0}

Let's find the direction vectors of these lines: d1⃗=⟨0,4,1⟩\vec{d_1} = \langle 0, 4, 1 \rangle and d2⃗=⟨3,−4,0⟩\vec{d_2} = \langle 3, -4, 0 \rangle .

Now, let's find the cross product of the direction vectors, which will give a vector that is perpendicular to both lines :

n⃗=d1⃗×d2⃗=⟨4,3,−12⟩\vec{n} = \vec{d_1} \times \vec{d_2} = \langle 4, 3, -12 \rangle

Let's find the vector connecting a point on line 1 to a point on line 2 :

c⃗=⟨2λ,3,−12⟩\vec{c} = \langle 2\lambda, 3, -12 \rangle

The shortest distance between the two lines is the projection of c⃗\vec{c} onto n⃗\vec{n} :

d=∣c⃗⋅n⃗∣n⃗∣∣=∣(2λ)(4)+(3)(3)−(12)(−12)16+9+144∣d = \left|\frac{\vec{c} \cdot \vec{n}}{|\vec{n}|}\right| = \left|\frac{(2\lambda)(4) + (3)(3) - (12)(-12)}{\sqrt{16 + 9 + 144}}\right|

We are given that the shortest distance is 13 :

13=∣8λ+15313∣13 = \left|\frac{8\lambda + 153}{13}\right|

∣8λ+153∣=169|8\lambda + 153| = 169

We have two cases :

1. 8λ+153=1698\lambda + 153 = 169

λ=168\lambda = \frac{16}{8}

2. 8λ+153=−1698\lambda + 153 = -169

λ=−3228\lambda = \frac{-322}{8}

Now, let's calculate 8∣∑λ∈Sλ∣8\left|\sum\limits_{\lambda \in S} \lambda\right| :

8∣168+−3228∣=8∣−3068∣=3068\left|\frac{16}{8} + \frac{-322}{8}\right| = 8\left|\frac{-306}{8}\right| = 306

Thus, the correct answer is Option A : 306.

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