1/2x3+1/3x4+1/基谨数4x5+1/5x6=1/2-1/搏首3+1/3-1/4+1/4-1/5+1/晌春5-1/6=1/2-1/6=1/3
1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1/2-1/6=1/3
5/6就是1-1/6