1.2b/2abc ,c/2abc
2.3x/3x(x-1) ,2(x-1)/3x(x-1)
3.9/3x-6,-2/3x-6
4.x-4/(x+1)(x-4)²,2(x+1)/(x+1)(x-4)²
5.2x/6(y-1),-2/6(y-1)
6.(x-1)/(x-1)²(x-2),2(x-2)/(x-1)²(x-2)
通分的意思就是把分母化成相同的部分,便于分子计算,比较