Let the lines L_1: = i+2 j+3 k+λ(2 i+3 j+4 k), λ ∈ mathbbR and L_2: =(4 i+ j)+μ(5 i+2 j+ k), μ ∈ mathbbR, intersect at the point R. Let P and Q be…
JEE Main 2026 — Mathematics Vectors & 3D Geometry
2026mcqhard
Let the lines L1:r=i^+2j^+3k^+λ(2i^+3j^+4k^),λ∈R and L2:r=(4i^+j^)+μ(5i^+2j^+k^),μ∈R, intersect at the point R. Let P and Q be the points lying on lines L1 and L2, respectively, such that ∣PR∣=29 and ∣PQ∣=347. If the point P lies in the first octant, then 27(QR)2 is equal to
Official previous-year question
Held on 24 Jan 2026 · Verified 6 Jul 2026.
Options
A
348
B
340
C
320
D
360
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Solution
Find R by solving L1=L2:
From 1+2λ=4+5μ, 2+3λ=1+2μ, 3+4λ=μ we get λ=−1, μ=−1, so R=(−1,−1,−1)
Point P on L1: P=(1+2λP,2+3λP,3+4λP) with ∣PR∣2=29