`1/1.3 + 1/3.5+1/5.7+….+1/107.109+1/109.111`

1 bình luận về “`1/1.3 + 1/3.5+1/5.7+….+1/107.109+1/109.111`”

1. 1/1.3+1/3.5+1/5.7+1/7.9+…+1/107.1/109

   =1/2.(2/1.3+2/3.5+2/5.7+2.7.9+….+2/107.109)

   =1/2.(1-1/3+1/3-1/5+1/5-1/7+1/7-1/9+…+1/107-1/109+1/109+1/111)

   =1/2.(1-1/111)

   =1/2 .(111/111-1/111)

   =1/2 . 110/111

   =55/111

   Trả lời