Answer: 2(|a|2 + |b|2).
- A 2|a|2
- B 2|b|2
- C 2(|a|2 + |b|2)
- D 4(|a|2 + |b|2)
Correct answer: C. 2(|a|2 + |b|2)
Explanation: Parallelogram law of cosines: |a+b|2 + |a-b|2 = 2(|a|2 + |b|2). The sum of squares of diagonals equals twice the sum of squares of the sides.
Triangle law of vector addition: placing vector b at the head of vector a, the diagonal from the start to the final head gives the resultant a + b.
Concept context
Vectors, dot product, cross product, and geometric applications