This is also correct, and it's consistent with what I
posted, so I'm not sure why you posted it. It focuses on
L/D, not power. The minimum for drag D is the same as the
max of L/D, but the minimum of power required occurs at a
different point. Am I missing something about why you
posted this?
This is not true. It depends on the engine. First if the Thrust
remains constant in relation to the speed, Minimum power required
equals minimum drag. But few engines give constant thrust output vs
speed. (Turbojet, turbofan, turboprop, reciprocating prop) The engine
giving an output almost constant is the turbojet, but I don't think it
is used in aviation anymore.