4.20. A, B, and C are three non-collinear, non-co-planar vectors. What can you say about the direction of A× (B × C)?

Hint: Recall the right-hand rule.
Step 1: Find the direction of B x C.
The direction of (B x C) will be perpendicular to the plane containing B and C by the right-hand rule.
Step 2: Find the direction of A x (B x C).
A x (B x C)will lie in the plane of B and C and is perpendicular to vector A.