\(A=\frac{5}{13}+\frac{-5}{7}+\frac{-20}{41}+\frac{8}{13}+\frac{-21}{41}\)
\(A=\left(\frac{5}{13}+\frac{8}{13}\right)+\left(-\frac{20}{41}+\frac{-21}{41}\right)+\left(-\frac{5}{7}\right)\)
\(A=1+\left(-1\right)-\frac{5}{7}\)
\(A=0+\left(-\frac{5}{7}\right)\)
\(A=-\frac{5}{7}\)
A=5/13-5/7-20/41+8/13-21/41
A=5/13+8/13-20/41-21/41-5/7
A=13/13-41/41-5/7
A=1-1-5/7
A=0-5/7
A=-5/7
Vậy A=-5/7
tk nha bn