A=5phan 13 + -5 phan 7=-20phan -41+8phan 13=-21phan41 B=-5 phan 9+8phan 15+-2phan11=4phan -9+7phan 15

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1. Đáp án:

    $A=\frac{-5}{7}\\
   B=\frac{-2}{11}$

   Giải thích các bước giải:

   $A=\frac{5}{13}+\frac{-5}{7}+\frac{20}{-41}+\frac{8}{13}+\frac{-21}{41}\\
   =\left ( \frac{5}{13}+\frac{8}{13} \right )+\frac{-5}{7}+\left ( \frac{-20}{41}+\frac{-21}{41} \right )\\
   =\frac{13}{13}+\frac{-5}{7}+\frac{-41}{41}\\
   =1+\frac{-5}{7}-1\\
   =\frac{-5}{7}\\
   B=\frac{-5}{9}+\frac{8}{15}+\frac{-2}{11}+\frac{4}{-9}+\frac{7}{15}\\
   =\left ( \frac{-5}{9}+\frac{4}{-9}\right )+\left ( \frac{8}{15}+\frac{7}{15} \right )+\frac{-2}{11}\\
   =\frac{-9}{9}+\frac{15}{15}+\frac{-2}{11}\\
   =-1+1+\frac{-2}{11}\\
   =\frac{-2}{11}$

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