先对式子化简 对分母x^2-y^2/x^2+4xy+4y^2=（x+2y）^2-y^2/x^2=(x+2y-y/x)(x+2y+y/x)原式=（x-y/x+2y)/(x+2y-y/x)(x+2y+y/x)=1/(x+2y+y/x)，再待数字计算
