Let a, b and be three non-zero non-coplanar vectors. Let the position vectors of four points A,B,C and D be a- b+ ,λ a-3 b+4, - a+2 b-3 and 2 a-4 b+6…
JEE Main 2023 — Mathematics Vectors & 3D Geometry
2023integermedium
Let a,b and c be three non-zero non-coplanar vectors. Let the position vectors of four points A,B,C and D be a−b+c,λa−3b+4c, −a+2b−3c and 2a−4b+6c respectively. If AB, AC and AD are coplanar, then λ is :
Official previous-year question
Held on 29 Jan 2023 · Verified 6 Jul 2026.
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Solution
Given,
a,b and c be three non-zero non-coplanar vectors,
Also the position vectors of four points A,B,C and D be a−b+c,λa−3b+4c, −a+2b−3c and 2a−4b+6c respectively,
So, AB=(λ−1)a−2b+3c
AC=−2a+3b−4c
AD=a−3b+5c
Now using the condition of coplanar we get,
∣λ−1−21−23−33−45∣=0
⇒(λ−1)(15−12)+2(−10+4)+3(6−3)=0
⇒(λ−1)=1⇒λ=2
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