0 bình luận về “Môn Toán Lớp 6: Tính nhanh 1/15 + 1/35 + 1/63 + 1/99 + 1/143”

1. 1/15 + 1/35 + 1/63 + 1/99 + 1/143

   = 1/(3.5) + 1/(5.7) + 1/(7.9) + 1/(9.11) + 1/(11.13)

   = 1/2 . (2/(3.5) + 2/(5.7) + 2/(7.9) + 2/(9.11) + 2/(11.13))

   = 1/2 . (1/3 – 1/5 + 1/5 – 1/7 + 1/7 – 1/9 + 1/9 – 1/11 + 1/11 – 1/13)

   = 1/2 . (1/3 – 1/13)

   = 1/2 . 10/39

   = 5/39

   #dtkc

   Trả lời
2. #Aka#

   1/15 + 1/35 + 1/63 + 1/99 + 1/143

   =1/3.5+1/5.7+1/7.9+1/9.11+1/11.13

   =1/2.(2/3.5+2/5.7+2/7.9+2/9.11+2/11.13)

   =1/2.(1/3-1/5+1/5-1/7+1/7-1/9+1/9-1/11+1/11-1/13)

   =1/2.(1/3-1/13)

   =1/2 . 10/39

   =5/39

   Trả lời