ABSTRACT
This chapter is the soul of the monograph. It covers the main theme, Lagrange’s approach, which is based on the principle of least action that leads to the introduction of the Lagrangian and the derivation of Lagrange’s equations. First, it introduces the reader to a tool called “calculus of variations”, and then uses this tool to calculate Lagrange’s equations from the principle of least action as well as from d’Alembert’s principle.
