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JEE Advanced · Mathematics · 31. 3D Geometry

Three lines are given by r=λi^, λR
r=μi^+j^,μR and
r=νi^+j^+k^,νR.
Let the lines cut the plane x+y+z=1 at the points A, B and C respectively. If the area of the triangle ABC is Δ then the value of 6Δ2 equals_________

  1. A 0.85
  2. B 0.14
  3. C 0.75
  4. D 0.9
Verified Solution

Answer & Solution

Correct Answer

(C) 0.75

Step-by-step Solution

Detailed explanation

Finding point A
Line r=λi^  and plane x+y+z=1
General point of line λ,0, 0, satisfy the plane
λ+0+0=1
λ=1
Hence, A(1, 0, 0) ...(i)
For point B
General point of line r=μi^+j^,  Bμ,μ,0
Satisfy the plane and μ+μ+0=1
μ=12
Point B12,12,0 ...(ii)
Similarly for point C
General point of line r=vi^+j^+k^, C(v, v, v)
Satisfy the plane v+v+v=1
v=13
Point C13,13,13 ....(iii)
AB=-12i^+12j^ and AC=-23i^+13j^+13k^
Now area of triangle ΔABC=12AB×AC
Δ=12ijk-12120-231313=12i^6+j^6+k^6=312 62=34=0.75
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