What is the cosine of the angle between two straight lines having direction ratios proportional to and ?

Answer and explanation

Correct answer: B.

  1. Step 1: Direction ratios are and .
  2. Step 2: Formula: .
  3. Step 3: Numerator: .
  4. Step 4: Since numerator is 0, (the lines are perpendicular).
Answer
.
Why not the others: Non-zero values result from arithmetic errors in the numerator sum; here exactly.

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