This is the first word in the name of a hybrid quantum-classical algorithm introduced by Peruzzo et al. with the most promising near-term potential for speeding up computational chemistry calculations. That “quantum eigensolver” described by this word takes advantage of the fact that the expectation of a Hermitian matrix is bounded below by its lowest eigenvalue. An approximation method named for this word minimizes the energy of a trial wavefunction with respect to a parameter. The Beltrami identity is key to a subfield of mathematical analysis whose name includes this plural noun, which uses the Euler–Lagrange equation to find the extrema of functionals (-5[1])like the action in Lagrangian mechanics. The brachistochrone problem (10[1])motivated the development of, for 10 points, the “calculus of” what word, (10[1])meaning small changes to functions? (10[1]0[8])■END■