$A_{}$ = $\cfrac{1}{3}$ - $\cfrac{3}{5}$ + $\cfrac{5}{7}$ - $\cfrac{7}{9}$ + $\cfrac{9}{11}$ - $\cfrac{11}{3}$ + $\cfrac{13}{15}$ + $\cfrac{11}{13}$ - $\cfrac{9}{11}$ + $\cfrac{7}{9}$ - $\cfrac{5}{7}$ + $\cfrac{3}{5}$ - $\cfrac{1}{3}$
= ($\cfrac{1}{3}$ - $\cfrac{1}{3}$) + (- $\cfrac{3}{5}$ + $\cfrac{3}{5}$) + ($\cfrac{5}{7}$ - $\cfrac{5}{7}$) + (- $\cfrac{7}{9}$ + $\cfrac{7}{9}$) + ($\cfrac{9}{11}$ - $\cfrac{9}{11}$) + (- $\cfrac{11}{3}$ + $\cfrac{11}{13}$) + $\cfrac{13}{15}$
= 0 + $\cfrac{13}{15}$
= $\cfrac{13}{15}$
Vậy $A_{}$ = $\cfrac{13}{15}$
Chúc bn học tốt!
Mong bn cho mik ctlhn và vote 5* ah
