∵x-3y=0∴x=3y (x²+y²)分之(x²-3xy+y²)=[(3y)²+y²]分之[(3y)²-3(3y)y+y²]=(9y²+y²)分之(9y²-6y²+y²)=(10y²)分之(4y²)=5分之2 很高兴...