原式=(x-6y)/(x+2y)(x-2y)+2y/x(x-2y)=(x²-6xy+2xy+4y²)/x(x+2y)(x-2y)=(x²-4xy+4y²)//x(x+2y)(x-2y)=(x-2y)²/x(x+2y)(x-2y)=(x-2y)/(x²+2xy)