分式的计算a/a-2÷a/(2-a)(a+3) 和2y/x-1+3y/1-x-y/1-x,

1.2y/x-1+3y/1-x-y/1-x
=2y/(x-1)-3y/(x-1)+y/(x-1)
=0
2.a/a-2÷a/(2-a)(a+3)
=a/(a-2)×[-(a-2)(a+3)/a]
=-(a+3)
=-a-3
3.2x+1/x+1÷1-4x²/1-x²乘1/x-1
=(2x+1)/(x+1)×(x+1)(x-1)/(2x+1)(2x-1)×1/(x-1)
=1/(2x-1)