【(1)/(x-y)+(1)/(x-y)】÷(2x)/(x²-2xy+y²)
=[2/(x-y)］÷2x/(x-y)²
=[2/(x-y)］*[(x-y)²/(2x)]
=(x-y)/x
1-【a-（1）/（1-a）】÷(a²-a+1)/(a²-2a+1)
=1-[(a-a²-1)/(1-a)]*[(a-1)²/(a²-a+1)]
=1-[(a²-a+1)/(a-1)]*[(a-1)²/(a^2-a+1)]
=1-(a-1)=2-a