原式=-1/2a²b+2a³+4a²b-5a²b-5a³=(-1/2a²b+4a²b-5a²b)+(2a³-5a³)=-3/2a²b-3a³当a=-1,b=-1/3时原式=-3/2×(-1)²×(-1/3)-3×(-1)³=-3/2×1×...