The evolution of a phragment of the theory of extremal
problems, the necessary conditions of extremum, is explained. Four problems
of Fermat, Lagrange, Euler and Pontryagin are presented and four classical
examples of Euclid, Kepler, Newton and Bernoulli are solved.
Keywords: Extremal problems, problems with and without
constraints, Lagrange multipliers, calculus of variation, optimal control,
Pontryagin's maximum principle.