A = $\dfrac{1}{2 . 3}$ + $\dfrac{2}{3 . 5}$ + $\dfrac{3}{5 . 8}$ + $\dfrac{4}{8 . 12}$ + $\dfrac{5}{12 . 17}$ + $\dfrac{6}{17 . 23}$ + $\dfrac{7}{23 . 30}$
A = $\dfrac{3-2}{2 . 3}$ + $\dfrac{5-3}{3 . 5}$ + $\dfrac{8-5}{5 . 8}$ + $\dfrac{12 - 8}{8 . 12}$ + $\dfrac{17 - 12}{12 . 17}$ + $\dfrac{23 - 17}{17 . 23}$ + $\dfrac{30 - 23}{23 . 30}$
A = $\dfrac{1}{2}$ - $\dfrac{1}{3}$ + $\dfrac{1}{3}$ - $\dfrac{1}{5}$ + $\dfrac{1}{5}$ - $\dfrac{1}{8}$ + $\dfrac{1}{8}$ - $\dfrac{1}{12}$ + $\dfrac{1}{12}$ - $\dfrac{1}{17}$ + $\dfrac{1}{17}$ - $\dfrac{1}{23}$ + $\dfrac{1}{23}$ - $\dfrac{1}{30}$
A = $\dfrac{1}{2}$ - $\dfrac{1}{30}$
A = $\dfrac{15}{30}$ - $\dfrac{1}{30}$
A = $\dfrac{15 - 1}{30}$
A = $\dfrac{14}{30}$
A = $\dfrac{7}{15}$
* Chú thích: Dấu "." là dấu nhân ah
