Let a=2 i+λ _1 j+3 k, b=4 i+(3-λ _2) j+6 k and =3 i+6 j+(λ _3-1) k be three vectors such that b=2 a and a is perpendicular to . Then a possible value…
JEE Main 2019 — Mathematics Vectors & 3D Geometry
2019mcqeasy
Let a=2i^+λ1j^+3k^,b=4i^+(3−λ2)j^+6k^ and c=3i^+6j^+(λ3−1)k^ be three vectors such that b=2a and a is perpendicular to c. Then a possible value of (λ1,λ2,λ3) is
Official previous-year question
Held on 10 Jan 2019 · Verified 6 Jul 2026.
Options
A
(−21,4,0)
B
(1,5,1)
C
(21,4,−2)
D
(1,3,1)
Did you get this right?
Sign in to track your attempts and accuracy.
Solution
Since b=2a, so 3−λ2=2λ1
λ2=3−2λ1...(1)
We know that if two vectors a1i^+b1j^+c1k^ and a2i^+b2j^+c2k^ are perpendicular, then a1a2+b1b2+c1c2=0
Since, a is perpendicular to c so
6+6λ1+3(λ3−1)=0
⇒6+6λ1+3λ3−3=0
⇒λ3=−1−2λ1...(2)
From equations (1) and (2), we get
(λ1,λ2,λ3)=(λ1,3−2λ1,−1−2λ1) where λ1∈R
⇒(−21,4,0) satisfies the above triplet.
Your note
Sign in to keep a private note on this question. Nothing you write is ever public.