  To identify the superconducting gap symmetry in CeCoIn5 (Tc=2.3 K), we
performed angle-resolved specific heat (C_\phi) measurements in a field rotated
around the c-axis down to very low temperatures 0.05Tc and detailed theoretical
calculations. In a field of 1 T, a sign reversal of the fourfold angular
oscillation in C_\phi has been observed at T ~ 0.1Tc on entering a
quasiclassical regime where the maximum of C_\phi corresponds to the antinodal
direction, coinciding with the angle-resolved density of states (ADOS)
calculation. The C_\phi behavior, which exhibits minima along [110] directions,
unambiguously allows us to conclude d_{x^2-y^2} symmetry of this system. The
ADOS-quasiclassical region is confined to a narrow T and H domain within T/Tc ~
0.1 and 1.5 T (0.13Hc2).
