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Question: Answered & Verified by Expert
If b=2i^-j^-k^, a=3i^+4j^-5k^ and b×(a×b)=a-kbl then kl|b| is
MathematicsVector AlgebraTS EAMCETTS EAMCET 2021 (05 Aug Shift 2)
Options:
  • A the orthogonal projection of b on a and equal to 750
  • B the orthogonal projection of a on b and equal to 76
  • C the orthogonal projection of b in the direction perpendicular to a and equal to 53
  • D the orthogonal projection of a in the direction perpendicular to b and equal to 7523
Solution:
2697 Upvotes Verified Answer
The correct answer is: the orthogonal projection of a on b and equal to 76

Given, b=2i^-j^-k^ and a=3i^+4j^-5k^

So, b×a×b=b·ba-b·ab=6a-7b=a-76b16  ...1

As given, b×(a×b)=a-kbl

Comparing with 1

we get, l=16k=76

So, klb=7616×6=76

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