The acute angle between the two planes and is:

Answer and explanation

Correct answer: B.

  1. Step 1: The angle between two planes is the angle between their normal vectors and .
  2. Step 2: Compute the scalar product: .
  3. Step 3: Compute magnitudes: , and . Thus .
Answer
.
Why not the others: corresponds to ; corresponds to ; requires orthogonal normals.

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