9y的平方-x的平方/x的平方+6xy+9y的平方÷x-3y/x的平方+3xy=(9y²-x²)/(x²+6xy+9y²)÷(x-3y)/(x²+3xy)=(3y+x)(3y-x)/(x+3y)²÷(x-3y)/[x(x+3y)]=(3y-x)/(x+3y)÷(x-3y)/[x(x+3y)]=(3y-...