  We study CP-violation in resonant three-body B -> DPP decays, where PP stands
for either Dpi, DK_S, pipi or piK_S. Analogously to the B -> 3pi channel and
the extraction of 2alpha, the first three channels are shown to measure
cos(2beta) in addition to sin(2beta), thus allowing to resolve the beta -> pi/2
-beta ambiguity, while the DpiK_S final state leads to a measurement of
2beta+gamma. The B0(t) -> D+D-pi0 channel via the interference between D**
orbitally excited resonances is taken as an example, although this
Cabibbo-suppressed decay suffers from irreducible penguin uncertainties. Then
two penguin-free and Cabibbo-dominant modes are proposed: B0(t) -> D+D-K_S with
the D_s** resonances, and B0(t) -> D0_CP pi+pi- with the D** plus the rho.
Finally, the B0(t) -> D+-pi-+K_S channel with the D_s** and K* resonances
provides a new clean method to measure the unusual angle 2beta+gamma. We
present in all cases a crude estimate of the number of cos(2beta) (respectively
2beta+gamma) sensitive events. We show that this number is an increasing
function of the resonance mass, a favorable situation compared to the more
extensively studied three-pion Dalitz plot. However, the poor detection
efficiency of the D mesons could pose a problem. As an annex and speculative
application of these Dalitz plot based methods, the penguin-dominated B0(t) ->
K_SK_SK_L decay also measures 2beta.
