添项减项法y³+7y²-8=y³-y²+8y²-8=y²(y-1)+8(y²-1)=y²(y-1)+8(y+1)(y-1)=(y-1)(y²+8y+8)=(y-1)(y+4+2v2)(y+4-2v2)(v为根号)祝你学习进步!