Vectors 2 Question 20

20. Let A,B and C be unit vectors. If AB=AC=0 and that the angle between B and C is π/6.

Then, A=±2(B×C).

(1981, 2M)

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Solution:

  1. Given, AB=AC=0

A is perpendicular to both B and C.

A=λ(B×C)

|A|=|λ||B×C|, where A,B,C are unit vectors.

|λ|=11sin30|λ|=2λ=±2

A=±2(B×C)

Hence, given statement is true.



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