Vectors satisfy and . What is ?

Answer and explanation

Correct answer: A.

.
  1. Step 1: Expand the cross product algebraically using bilinearity and skew-symmetry ( and ):
  2. Step 2: Find between the vectors using the definition of the dot product: .
  3. Step 3: Compute .
  4. Step 4: Evaluate the required magnitude: .
Answer
.
Why not the others: results from an algebraic sign miscalculation ( instead of ), giving coefficient instead of .

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