  Isoperimetric problems consist in minimizing or maximizing a cost functional
subject to an integral constraint. In this work, we present two fractional
isoperimetric problems where the Lagrangian depends on a combined Caputo
derivative of variable fractional order and we present a new variational
problem subject to a holonomic constraint. We establish necessary optimality
conditions in order to determine the minimizers of the fractional problems. The
terminal point in the cost integral, as well the terminal state, are considered
to be free, and we obtain corresponding natural boundary conditions.
