原式=1﹣1/2+﹙1﹣1/6﹚+﹙1﹣1/12﹚+﹙1﹣1/20﹚+﹙1﹣1/30﹚=5-﹙1/2
+1/6+1/12+1/20+1/30﹚=5-﹙1/2+1/2-1/3+1/3-1/4+1/4-1/5﹢
1/5-1/6﹚=4+1/6=25/6