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Question: Answered & Verified by Expert
Let a=i^+4j^+2k^,b=3i^-2j^+7k^ and c=2i^-j^+4k^. If a vector d satisfies d×b=c×b and d·a=24, then d2 is equal to
MathematicsVector AlgebraJEE MainJEE Main 2023 (13 Apr Shift 1)
Options:
  • A 323
  • B 423
  • C 313
  • D 413
Solution:
2205 Upvotes Verified Answer
The correct answer is: 413

We have been given that

d×b=c×b

(d-c)×b=0

d-c=λb  (dc)

d=c+λb

It is given that a·d=24 

a·c+λb·a=24

6+λ(3-8+14)=24

9λ=18

λ=2

d=c+2b

d=8i^-5j^+18k^

|d|2=64+25+324=413

Hence, this is the correct option.

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