bằng 3.141939849 kết bạn với mình nhé
Ta có : B = 4 / 2. 5 + 4 / 5 . 8 + 4 / 8 . 11 + 4 / 11 . 14
= 4 ( 1 / 2 . 5 + 1 / 5 . 8 + 1 / 8 . 11 + 1 / 11 . 14 )
= 4 . [ 1/3 ( 1 /2 - 1/5 + 1/5 - 1/8 + 1/8 - 1/ 11 + 1/11 - 1/14 )]
= 4 / 3 ( 1/ 2 - 1/14 )
= 4/3 . 3/7
= 4 / 7
Vậy B = 4 / 7
B = \(\frac{4}{2\times5}+\frac{4}{5\times8}+\frac{4}{8\times11}+\frac{4}{11\times14}\)
B = \(\frac{4}{10}+\frac{4}{40}+\frac{4}{88}+\frac{4}{154}\)
B = \(\frac{1}{73}\)\(\left(\frac{4}{292}\right)\)
