One reason that so many students struggle with the chain rule is that they never really got the point of composition in the first place. Sure they can “put one function inside another,” but they are missing this essential point:
Composite functions appear in situations where the value of one quantity is determined by another, which in turn is determined by another.
Functions appear in situations where the value of one quantity is determined by the value of another.
Understanding composition this way builds a natural bridge between related rates and the idea of composition. For example, consider the following scenarios:
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