Tính `B= 1/2.4 + 1/4.6 + … + 1/16.18 + 1/18.20`

0 bình luận về “Tính `B= 1/2.4 + 1/4.6 + … + 1/16.18 + 1/18.20`”

1. `B=1/(2.4) +1/(4.6) +…….+1/(16.18) +1/(18.20)`

   `B= (2/(2.4) +2/(4.6) +…….+2/(16.18) +2/(18.20)) : 2`

   `B= (1/2-1/4+1/4-1/6 +………..+1/16-1/18+1/18 – 1/20):2`

   `B= ( 1/2-1/20) : 2`

   `B= 9/20 : 2`

   `B=9/20  . 1/2`

   `B=9/40`  

          $\text{Xin hay nhất}$

    

   Trả lời

2. B = 1/2 . ( 2 / 2.4 + 2/ 4.6 + …. + 2/18. 20)

   B = 1/2 . ( 1/2 – 1/4 + 1/4 – 1/6 +…+ 1/18 – 1/20 )

   B = 1/2 . ( 1/2 –  1/20 )

   B = 1/2 .  11/ 20

   B = 11/40 

   Trả lời