Answer: -12.
- A -12
- B 0
- C 5
- D -5
Correct answer: A. -12
Explanation: Coplanar → scalar triple product = 0. det[[2,−1,k],[1,2,−1],[0,1,2]] = 2(4+1)−(−1)(2−0)+k(1−0) = 10+2+k = 0. So k = −12. Answer: k = −12.
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