Đáp án:
A = $\frac{-5}{259}$
Giải thích các bước giải:
A = $\frac{-1}{91}$ + $\frac{-1}{247}$ + $\frac{-1}{475}$ + $\frac{-1}{775}$ + $\frac{-1}{1147}$
= $\frac{1}{6}$ . 6 . ( $\frac{-1}{91}$ + $\frac{-1}{247}$ + $\frac{-1}{475}$ + $\frac{-1}{775}$ + $\frac{-1}{1147}$)
= $\frac{1}{6}$ . ( $\frac{-6}{91}$ + $\frac{-6}{247}$ + $\frac{-6}{475}$ + $\frac{-6}{775}$ + $\frac{-6}{1147}$ )
= $\frac{1}{6}$ . ( $\frac{-6}{7.13}$ + $\frac{-6}{13.19}$ + $\frac{-6}{19.25}$ + $\frac{-6}{25.31}$ + $\frac{-6}{31.37}$ )
= $\frac{1}{6}$ . ( $\frac{-1}{7}$ - $\frac{-1}{13}$ + $\frac{-1}{13}$ - $\frac{-1}{19}$ + $\frac{-1}{19}$ - $\frac{-1}{25}$ + $\frac{-1}{25}$ - $\frac{-1}{31}$ + $\frac{-1}{31}$ - $\frac{-1}{37}$ )
= $\frac{1}{6}$ . ($\frac{-1}{7}$ - $\frac{-1}{37}$ )
= $\frac{1}{6}$ . $\frac{-30}{259}$
A = $\frac{-5}{259}$
