Let a → = 3 i ^ + 2 j ^ + x k ^   and b → = i ^ - j ^ + k ^ , for some real x . Then the…

Let a→=3i^+2j^+xk^  and b→=i^-j^+k^, for some real x. Then the condition for a→×b→ =r to follow
  1. 0<r≤ 32
  2. r≥ 532
  3. 32<r≤332
  4. 3 32<r<532

Solution

As, We know that a→×b→=i^j^k^32x1-11
=2+xi^+x-3j^-5k^

a→×b→=4+x2+4x+x2+9-6x+25

=2x2-2x+38

Therefore, we have
⇒a→×b→≥752

⇒a→×b→≥532

Asked in: JEE Main 2019 (08 Apr Shift 2)

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