Noting the similarities between two of these concepts in mechanics and optics is the basis of the path integral formulation.
One of these concepts was applied to geodesic curvature by Hertz, but started as an application of least- squares to Z, or the "constraint," and was derived by Gauss. In quantum mechanics, one of these ideas centering on the T-matrix is used to derive the Lippman-Schwinger equation. Another of these ideas was derived by conceiving of Newton's second law in terms of an "inertial force," and is based on a vanishing "virtual work" for reversible displacements. That one of these ideas is named for (*) D'Alembert. Noting the similarities between two of these concepts in mechanics and optics is the basis of the path integral formulation. The use of these concepts is contrasted with, but mathematically equivalent to, Newtonian vectorial mechanics. One of these concepts can be used to derive the Euler-Lagrange equations by assuming that a given motion minimizes the action. For 10 points, name these constraints on the equations of motion, which can be derived using their namesake "calculus."
One of these concepts was applied to geodesic curvature by Hertz, but started as an application of least- squares to Z, or the "constraint," and was derived by Gauss.
variational principles [accept related answers with "variation" in them, including calculus of variations; prompt on "principles in physics" or similar answers]