“…More precisely, without limiting our investigation to convex costs as in Lee [16], the current framework is more comprehensive than in Schmitendorf [6], Hestenes [15], Udrişte and Ţevy [17], or Treanţȃ [2] both by the inclusion of integral functionals of multiple and curvilinear type as constraints and by the inclusion of new proofs. Additionally, compared with a very recent research paper (see Treanţȃ [18]), the present paper takes into account the isoperimetric constraints defined by multiple integral functionals (see Section 2.2). Moreover, due to the very important physical applications of the functionals used (for example, mechanical work), this paper is a very good starting point for researchers in the field of applied mathematics that deal with the design, theory, and applications of mathematics, management science, operations research, optimal control science, and economics.…”