Maclaurin series
Any smooth function can be approximated near by a polynomial whose derivatives match it there: . Standard series for , , , and combine by substitution, multiplication and differentiation.
≈ 45 minTaylor series, L'Hôpital and Leibniz
Expanding about instead of gives the Taylor series . Series also crack "" limits (as does L'Hôpital's rule), and Leibniz's theorem gives the th derivative of a product like a binomial expansion.
≈ 50 min