Question

$\mathbf{a} \times (\mathbf{b} \times \mathbf{c})$ is coplanar with

• A. b and c
• B. c and a
• C. a and b
• D. a, b and c

Answer 1

Answer: (A)

b and c

Answer 2

$\mathbf{b} \times \mathbf{c}$ is a vector perpendicular to $\mathbf{b},\mathbf{c}.$

Therefore, $\mathbf{a} \times (\mathbf{b} \times \mathbf{c})$ is a vector again in plane of $\mathbf{b},\mathbf{c}.$