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ExamsJEE MainMaths

A vector a = α î + 2ĵ + β k̂ lies in the plane determined by b = î + ĵ and c = ĵ + k̂, and it bisects the angle between b and c. Which of the following can be the values of α and β?

  1. α = 2, β = 2
  2. α = 1, β = 2
  3. α = 2, β = 1
  4. α = 1, β = 1

Correct answer: α = 1, β = 1

Solution

Since |b|=|c|=sqrt2, the internal bisector is along b+c=(1,2,1). For a=(alpha,2,beta) to be parallel to (1,2,1) with middle component 2, take the vector (1,2,1) itself, giving alpha=1, beta=1.

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