Question

2分之一加6分之一加12分之一加到72分之一……加4950分之1等于多少？

Answer 1

裂项法
1/2+1/6+1/12+1/20+1/30+1/42+1/56+1/63+1/72+……+1/4950
=1-1/2+1/2-1/3+1/3-1/4+1/4-1/5+……+1/49-1/50
=1-1/50
=49/50