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Let the square of the shortest distance between the lines L1:r⃗=(i^+2j^−4k^)+λ(2i^+3j^+6k^)L_1: \vec{r} = (\hat{i}+2\hat{j}-4\hat{k}) + \lambda(2\hat{i}+3\hat{j}+6\hat{k}) and L2:r⃗=(3i^+3j^−5k^)+μ(2i^+3j^+6k^)L_2: \vec{r} = (3\hat{i}+3\hat{j}-5\hat{k}) + \mu(2\hat{i}+3\hat{j}+6\hat{k}) is mn\dfrac{m}{n}, where gcd⁡(m,n)=1\gcd(m,n)=1. Then m+nm+n is equal to:

Solution

✅ Correct Option: 4

Both lines share direction d⃗=(2,3,6)\vec d = (2,3,6), so they are parallel and the distance formula for parallel lines applies with a⃗2−a⃗1=(2,1,−1)\vec a_2 - \vec a_1 = (2,1,-1).

d⃗×(a⃗2−a⃗1)=(−9,14,−4)\vec d \times (\vec a_2-\vec a_1) = (-9,14,-4), of squared length 293293, while ∣d⃗∣2=49|\vec d|^2 = 49.

So m/n=293/49m/n = 293/49 and m+n=342m+n = 342.

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