B = 1.2 + 2.3 + 3.4 +… + 98.99

1 bình luận về “B = 1.2 + 2.3 + 3.4 +… + 98.99”

1. Ta có:

   B = 1.2 + 2.3 + 3.4 + ….. + 98.99

   => 3B = 3.(1.2 + 2.3 + 3.4 + ….. + 98.99)

   => 3B = 1.2.(3 – 0) + 2.3.(4 – 1) + …. + 98.99.(100 – 97)

   => 3B = 1.2.3 – 1.2.3 + 2.3.4 – 2.3.4 + ….. + 98.99.100

   => 3B = 98.99.100

   => B = (98.99.100)/3 = 485100

   Vậy B = 485100

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