Let a → = i ^ + 4 j ^ + 2 k ^ , b → = 3 i ^ - 2 j ^ + 7 k ^ and c → = 2 i ^ - j ^ + 4 k ^ …

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
  1. 323
  2. 423
  3. 313
  4. 413

Solution

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.

Asked in: JEE Main 2023 (13 Apr Shift 1)

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