\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)
\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(\frac{3}{7}-\frac{3}{7}\right)+\left(\frac{2}{11}-\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)
\(B=0-\frac{9}{16}\)
\(B=-\frac{9}{16}\)
\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)
\(B=\left(\frac{1}{5}-\frac{1}{5}\right)+\left(-\frac{3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}-\frac{5}{9}\right)+\left(-\frac{2}{11}+\frac{2}{11}\right)+\left(\frac{7}{13}-\frac{7}{13}\right)-\frac{9}{16}\)
\(B=0+0+0+0-\frac{9}{16}\)
\(B=0-\frac{9}{16}\)
\(B=-\frac{9}{16}\)
\(B=\frac{1}{5}-\frac{3}{7}+\frac{5}{9}-\frac{2}{11}+\frac{7}{13}-\frac{9}{16}-\frac{7}{13}+\frac{2}{11}-\frac{5}{9}+\frac{3}{7}-\frac{1}{5}\)
\(B=\frac{1}{5}+\left(-\frac{3}{7}\right)+\frac{5}{9}+\left(-\frac{2}{11}\right)+\frac{7}{13}+\left(-\frac{9}{16}\right)+\left(\frac{-7}{13}\right)+\frac{2}{11}+\left(\frac{-5}{9}\right)+\frac{3}{7}+\left(-\frac{1}{5}\right)\)
\(B=\left(\frac{1}{5}+\frac{-1}{5}\right)+\left(\frac{-3}{7}+\frac{3}{7}\right)+\left(\frac{5}{9}+\frac{-5}{9}\right)+\left(\frac{7}{13}+\frac{-7}{13}\right)+\frac{-9}{16}\)
\(B=0+0+0+0+\frac{-9}{16}\)
\(B=-\frac{9}{16}\)
Vậy \(B=\frac{-9}{16}\)