Bài 1 : a) A = 1 + 1/1.2 + 1/2.3 +….+ 1/202.203 b) B = 1 – 1/1.3 + 1/3.5 + 1/5.7 +….+ 1/209 . 211 Mn giúp em với,em cảm ơ

2 bình luận về “Bài 1 : a) A = 1 + 1/1.2 + 1/2.3 +….+ 1/202.203 b) B = 1 – 1/1.3 + 1/3.5 + 1/5.7 +….+ 1/209 . 211 Mn giúp em với,em cảm ơ”

1. a,

   Ta có: A = 1 + 1/(1.2) + 1/(2.3) + … + 1/(202.203)

   => A = 1 + 1 – 1/2 + 1/2 – 1/3 + … + 1/(202) – 1/(203)

   => A = 1 + 1 – 1/(203)

   => A = 2 – 1/(203)

   => A = (405)/(203)

   Vậy A = (405)/(203)

   b, 

   Ta có: B = 1 – 1/(1.3) + 1/(3.5) + 1/(5.7) + …. + 1/(209.211)

   => B = 1 – 1/3 + 1/2 (1/3 – 1/5 + 1/5 – 1/7 + … + 1/(209) – 1/(211))

   => B = 2/3 + 1/2 .(1/3 – 1/(211))

   => B = 2/3 + 1/2 . (208)/(633)

   => B = 2/3 + (104)/(633)

   => B = (526)/(633)

   Vậy B = (526)/(633)

   $#duong612009$

   Trả lời
2. Gửi e

   a. A = 1 + 1/(1.2) + 1/(2.3) + … + 1/(202.203)

   = 1 + 1 – 1/2 + 1/2 – 1/3 + … + 1/(202) – 1/(203)

   = 2 – 1/(203)

   = (405)/(203)

   b. B = 1 – 1/(1.3) + 1/(3.5) + 1/(5.7) + …. + 1/(209.211)

   = 1 – 1/3 + 1/2 (1/3 – 1/5 + 1/5 – 1/7 + … + 1/(209) – 1/(211))

   = 2/3 + 1/2 . (208)/(633)

   = (526)/(633)

   Trả lời