Đáp án:
$A=\frac{-5}{7}\\
B=\frac{-2}{11}$
Giải thích các bước giải:
$A=\frac{5}{13}+\frac{-5}{7}+\frac{20}{-41}+\frac{8}{13}+\frac{-21}{41}\\
=\left ( \frac{5}{13}+\frac{8}{13} \right )+\frac{-5}{7}+\left ( \frac{-20}{41}+\frac{-21}{41} \right )\\
=\frac{13}{13}+\frac{-5}{7}+\frac{-41}{41}\\
=1+\frac{-5}{7}-1\\
=\frac{-5}{7}\\
B=\frac{-5}{9}+\frac{8}{15}+\frac{-2}{11}+\frac{4}{-9}+\frac{7}{15}\\
=\left ( \frac{-5}{9}+\frac{4}{-9}\right )+\left ( \frac{8}{15}+\frac{7}{15} \right )+\frac{-2}{11}\\
=\frac{-9}{9}+\frac{15}{15}+\frac{-2}{11}\\
=-1+1+\frac{-2}{11}\\
=\frac{-2}{11}$
