x减2y分之x减y除以x方减4xy加4y方分之x方减y方
=[(x-y)/(x-2y)]×[(x-2y)²/(x+y)(x-y)]
=(x-2y)/(x+y)
=[(1+√2-2(1-√2)]/(1+√2+1-√2)
=(1+√2-2+2√2)/2
=(-1+3√2)/2