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Why is the derivative of a composition a product, and what has to happen to the inside variable for the cancellation to survive the limit?
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読み込み中…
Composition as substitution, with a named intermediate variable
Write as two steps, then , note the shorthand, and record that the last step substitutes back.
The one-line derivation of
Write , cancel , record the limit step as , and state both and .
Worked example
Take and , multiply them, and substitute back to finish at .
and the shortcut without the middle variable
With and , reach , then redo it without naming , differentiating the outside function, leaving the inside expression alone, and multiplying by its derivative.