1/3m-3/2n-5/6n-1/6m
其中m=6,n=2
1/3m-3/2n-5/6n-1/6m=1/18-3/4-5/12-1/36=2/36-27/36-15/36-1/36=(2-27-15-1)/36=-41/36=-7/6