1、化简:(x²+1/x²-1)-(x-2/x-1)÷(x-2/x)
=(x²+1)/(x²-1)-x/(x-1)
=(x²+1-x²-x)/(x-1)
=(1-x)/(x-1)
=-1
2、定义运算☆,其规则为：a☆b=1/a-1/b,求(x-1)☆(1-x)=2/3中x的的值
1/(x-1)-1/(1-x)=2/3
2/(x-1)=2/3
x-1=3
x=4
3、已知a/b=1/3,分式a+b/a-b的值为
a/b=1/3
b=a
(a+b)/(a-b)
=(a+3a)/(a-3a)
=4a/(-2a)
=-2