a+2/a^2-4=1/(a-2)
3a/5xy=(6a^2)/10axy
计算；
3/x-2/5y=(15y-2x)/5xy
9m^2/-3m-n+n^2/n+3m
a^2/a-b-a-b=[a^2-(a-b)(a+b)]/(a-b)=(a^2-a^2+b^2)/(a-b)=b^2/(a-b)
(xy-y^2)÷x-y/xy
=[y(x-y)]*[xy/(x-y)]
=xy^2
解方程；
1/x+1=2/x-1
两边乘(x+1)(x-1)
1*(x-1)=2(x+1)
x-1=2x+2
x=-3
经检验,x=-3是方程的解
2x/2x+5+5/5x-2=1
两边乘(2x+5)(5x-2)
2x(5x-2)+5(2x+5)=(2x+5)(5x-2)
10x^2-4x+10x+25=10x^2+21x-10
15x=35
x=7/3
经检验,x=7/3是方程的解
1/x-2+3=x-1/x-2
两边乘x-2
1-3(x-2)=x-1
1-3x+3=x-1
4x=5
x=5/4
经检验,x=5/4是方程的解