A line makes angles with the positive axes. What is the value of ?

Answer and explanation

Correct answer: B.

  1. Step 1: We know that the sum of squares of the direction cosines is unity: .
  2. Step 2: Use the trigonometric identity for each angle.
  3. Step 3: Substitute: .
Answer
.
Why not the others: is ; assumes for all three angles; is physically impossible for orthogonal axes.

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