1/1x2+1/2x3+1/3x4.1/49x50
问题描述：
1/1x2+1/2x3+1/3x4.1/49x50
答
等于49/50.用裂项法.要是还不清楚问我.
=1-1/2+1/2-1/3+1/3-1/4+...+1/49-1/50
=1-1/50
=49/50