Đáp án: ("."là nhân nhé bn)
$\dfrac{2}{1.3}$+$\dfrac{2}{3.5}$ +$\dfrac{2}{5.7}$ +$\dfrac{2}{7.9}$ +$\dfrac{2}{9.11}$ +$\dfrac{9}{11.13}$ +$\dfrac{2}{13.15}$
=1-$\dfrac{1}{3}$-$\dfrac{1}{5}$ +$\dfrac{1}{5}$ -$\dfrac{1}{7}$ +$\dfrac{1}{7}$ -$\dfrac{1}{9}$ +$\dfrac{1}{9}$-$\dfrac{1}{11}$+$\dfrac{1}{11}$-$\dfrac{1}{13}$+$\dfrac{1}{13}$-$\dfrac{1}{15}$
=1-$\dfrac{1}{15}$
=$\dfrac{15}{15}$-$\dfrac{1}{15}$
=$\dfrac{14}{15}$
@ChichooKim95
