I've learned that Newtonian mechanics and Lagrangian mechanics are equivalent, and Newtonian mechanics can be deduced from the least action principle.
Could the least action principle min∫L(t,q,q′)dt in mechanics be deduced from Newtonian F=ma?
Sorry if the question sounds beginnerish
Answer
You also need an expression for the Lagrangian, which in classical mechanics is L=T−U
Where T is the kinetic energy and U is the potential energy.
Provided that you can associate a potential U to the force →F such that →F=−→∇U (such a force is said to be conservative), the principle of least action and Newton second's law are equivalent.
The demonstration for a single particle in 1D (T=mv2x/2, F=−dU(x)/dx) is actually a good exercise.
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