Final answer:
Hexagon's grandson likely used a mathematical concept to line up his toy soldiers, moving them one at a time to apply a strategy, rule, or formula in a stepwise manner.
Step-by-step explanation:
The question implies that Hexagon's grandson lined up his toy soldiers in a specific pattern or sequence, most likely related to a mathematical concept. Since no further context is provided, one can assume it may involve principles of counting, arranging, or perhaps even geometric progression if we consider 'Hexagon' as a reference to a geometric shape.
The mention of moving them one at a time suggests that the grandson is implementing a strategy, rule, or formula that requires sequential steps. This approach is common in problem-solving activities in math where each move or change is stepwise and deliberate, allowing the observer to follow the logic and reasoning behind the arrangement.