We can use the right-hand rule to determine the direction and sign of a cross product.
- Make a gun gesture but bend the middle finger anticlockwise so that it’s perpendicular to the index finger.
- The index finger is the first operand and middle finger is the second operand.
- Orientate the hand as in the problem—either use an existing image or imagine your hand in a 3D coordinate system. The cross product is in the direction of the thumb.
- If B is anticlockwise from A (in which case the thumb points up), the product is positive, and vice versa (clockwise, and thumb points down).