Linked from
The 13 pages that link to Differential calculus, each with the reason it gives.
Condition numberNarrower topic: Derivatives yield local condition numbers for smooth functions.
InfinitesimalNarrower topic: Infinitesimal changes provide one way to formulate the derivative.
Related ratesNarrower topic: Related rates applies derivatives to quantities that vary together.
Leibniz notationRelated: The symbols dy and dx denote changes whose relationship dy/dx expresses.