Consider the lines L_1: x-1= y-2= z and L_2: x-2= y= z-1. Let the feet of the perpendiculars from the point P(5,1,-3) on the lines L_1 and L_2 be Q…
JEE Main 2025 — Mathematics Vectors & 3D Geometry
2025mcqhard
Consider the lines L1:x−1=y−2=z and L2:x−2=y=z−1. Let the feet of the perpendiculars from the point P(5,1,−3) on the lines L1 and L2 be Q and R respectively. If the area of the triangle PQR is A , then 4A2 is equal to :
Official previous-year question
Held on 7 Apr 2025 · Verified 6 Jul 2026.
Options
A
139
B
147
C
151
D
143
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Solution
L1:1x−1=1y−2=2z−0 Let Q(λ+1,λ+2,λ)PQ=(λ−4,λ−1,λ+3)PQ⋅m=0
⇒⇒λ−4+λ+1,λ+3=03λ=0λ=0
L2:1x−2=1y−0=2z−1 Let R(μ+2,μ,μ+1)PR=(μ−3,μ−1,μ+4)PR⋅n=0μ−3+μ−1+μ+4=0=μ=0
Area of △PQR(A)=21∣PQ×PR∣A=21∣(−4i^+j^+3k^)×(−3i^+j^+4k^)∣A=21∣7(i^+j^+k^)∣i^−4−3j^1−1k^34=7i^+7j^+7k^4A2=49×3=147
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