原式=1/1*2+1/2*3+1/3*4+1/4*5+1/5*6=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1-1/6=5/6
=1/1*2+1/2*3+1/3*4+1/4*5+1/5*6=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+1/5-1/6=1-1/6=5/6
原式等于：1-2分之1+2-
