-a³+2b³－3ab+2= - (a³-2b³+3ab-2)=2－a³－(3ab-2b³)
若a-b=4,b-c=1,c-d=－2,则a-d=(a-b)+(b-c)+(c-d)=4+1-2=3
若2x²-6x+1=0,则6+3x-x²=(1/2)(12+6x-2x²)=(1/2)[12-(2x²-6x)]=(1/2)[12-(-1)]=13/2