  Quantum-correlated psi(3770)->DDbar decays collected by the CLEO-c experiment
are used to perform measurements of F+, the fractional CP-even content of the
self-conjugate decays D->pi+pi-pi0 and D->K+K-pi0. Values of 0.973+/-0.017 and
0.732+/-0.055 are obtained for pi+pi-pi0 and K+K-pi0, respectively. The high
CP-even content of D->pi+pi-pi0, in particular, makes this a promising mode for
improving the precision on gamma and for measurements of CP violation in D
decay.
