题目内容：

1.已知正数x,y满足x2-y2=2xy,求(x-y)/(x+y)的值
2.若x2+xy-2y2=0则(x2+3xy-2y2)/x2-2y2)=_________
3.先化简,后求值：(3-x)/(x-2)除以（x+2-2/(x-2)）,其中x=2√2