1.a+2b/2a-b=9/5 ,则5(a+2b)=9(2a-b),则5a+10b=18a-9b,则13a=19b,所以a:b=19:132.x-1/x（x-1）=1/x成立的条件是x≠13.1/x-1/y=2 ,则y/(xy)-x/(xy)=2,则(y-x)/(xy)=2,所以y-x=2xy,所以x-y=-2xy 3x+5xy-3y/x-xy-y=5x...