Q74 / 160 · TS EAMCET 2022 (18 Jul Shift 1) · Mathematics

Let a→=i^+j^+k^, b→=i^-2j^+k^,c→=i^+3j^-2k^,d→=2i^+j^-k^ be four vectors and let l=b→·c→ and m=b→·a→. Then mb→+Ia→b→d→

  • A
    79
  • Correct answer
    B
    -63
  • C
    0
  • D
    1

Solution

Given:

a→=i^+j^+k^

b→=i^-2j^+k^

c→=i^+3j^-2k^

d→=2i^+j^-k^

Also,

l=b→·c→ 

⇒l=i^-2j^+k^·i^+3j^-2k^

⇒l=-7

And,

m=b→·a→

⇒m=i^-2j^+k^·i^+j^+k^

⇒m=0

We have,

mb→+Ia→b→d→

=-7a→b→d→

=-7a→b→d→

=-7i^+j^+k^·i^-2j^+k^×2i^+j^-k^

=-7i^+j^+k^·i^+3j^+5k^

=-7×1+3+5

=-63

Hence, the correct answer is option: 'B'.

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