I don't know what 10 problems your professor had in mind but his comment was either in jest or perhaps was made from a narrow mathematical viewpoint: variationa

I don't know what 10 problems your professor had in mind but his comment was either in jest or perhaps was made from a narrow mathematical viewpoint: variational principles form the basis of much of Physics, e.g. Hamilton's principle, Fermat's principle, etc. As a side note, for those of you who, like myself, have puzzled how Euler-Lagrange Equations are drived, the answers given to this question are priceless: http://physics.stackexchange.com/questions/885/why-does-calculus-of-variations-work http://physics.stackexchange.com/questions/885/why-does-calc...