In this paper we study isoperimetric problems of the calculus of variations
with left and right Riemann-Liouville fractional derivatives. Both situations
when the lower bound of the variational integrals coincide and do not coincide
with the lower bound of the fractional derivatives are considered.Comment: Submitted 02-Oct-2009; revised 30-Jun-2010; accepted 10-May-2011; for
publication in the journal Acta Mathematica Scienti