B=7/15+7/35+7/63+……………….++7/399+7/483. Tìm B Các anh chị giúp e ạ . Trong hôm nay em phải nộp rồi

$B$ = $\frac{7}{15}$ + $\frac{7}{35}$ + $\frac{7}{63}$ + … + $\frac{7}{399}$ + $\frac{7}{483}$

$B$ = $\frac{7}{3.5}$ + $\frac{7}{5.7}$ + $\frac{7}{7.9}$ + … + $\frac{7}{19.21}$ + $\frac{7}{21.23}$

$B$ = $\frac{1}{3}$ – $\frac{1}{5}$ + $\frac{1}{5}$ – $\frac{1}{7}$ + $\frac{1}{7}$ – $\frac{1}{9}$ + … + $\frac{1}{19}$ – $\frac{1}{21}$ + $\frac{1}{21}$ – $\frac{1}{23}$ 

$B$ = $\frac{1}{3}$ – $\frac{1}{23}$ 

$B$ = $\frac{20}{69}$ 

Học tốt !