1、y²-y+4分之1=(y-2分之1)²2、3a²+6ab+3b²=3(a²+2ab+b²)=3(a+b)²3、xy³-2x²y²+x³y=xy(y²-2xy+x²)=xy(y-x)²4、-a³+a²b-4分之1ab&...-x-2xy-y²-x²-2xy-y²=-(x²+2xy+y²)=-(x+y)²