x=1+√2,y=1-√2
x+y=2 x-y=2√2
[（1/（x-y)+1/(x+y)]-【2y/（x的平方-2xy+y的平方）】
=[（x+y+x-y/（x-y)(x+y)]-【2y/（x-y）^2】
=[2(1+√2)/2*2√2]-【2(1-√2)/（2√2）^2】
=[(1+√2)/2√2]-【2(1-√2)/8】
=[(2+√2)/4]-【(1-√2)/4】
=(1+2√2)/4难道不需要化到最简再带入么x=1+√2，y=1-√2x+y=2x-y=2√2[（1/（x-y)+1/(x+y)]-【2y/（x的平方-2xy+y的平方）】 =[（x+y+x-y/（x-y)(x+y)]-【2y/（x-y）^2】=[（2x/（x-y)(x+y)]-【2y/（x-y）^2】=(2x(x-y)-2y(x+y))/(x+y)（x-y）^2=(2x^2-2xy-2xy-2y^2)/(x+y)（x-y）^2=2(x^2-2xy-y^2)/(x+y)（x-y）^2应该化成最简，当时看化简意义不大，才直接代入x、y的值