Tính bằng cách thuận tiện nhất: =1/6+1/10+1/15+1/21+1/28+1/36

1 bình luận về “Tính bằng cách thuận tiện nhất: =1/6+1/10+1/15+1/21+1/28+1/36”

1. A = 1/6 + 1/10 + 1/15 + 1/21 + 1/28 + 1/36

   1/2 A = (1/6+1/10+1/15+1/21+1/28+1/36) × 1/2

   = 1/12+1/20+1/30+1/42+1/56+1/72

   = 1/3.4 + 1/4.5 + 1/5.6 + 1/6.7 + 1/7.8 + 1/8.9

   = 1/3 – 1/4 + 1/4 -1/5 + 1/5 – 1/6 + 1/6 – 1/7 + 1/7 – 1/8 + 1/8 – 1/9

   = 1/3 – 1/9

   = 3/9 – 1/9

   = 2/9

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