Đáp án:
a, $\dfrac{5}{6}$ và $\dfrac{7}{9}$
$\text{$\dfrac{5}{6}$ = $\dfrac{5 × 9}{6 × 9}$ = $\dfrac{15}{18}$}$
$\text{$\dfrac{7}{9}$ = $\dfrac{7 × 6}{9 × 6}$ = $\dfrac{14}{18}$}$
$\text{$\dfrac{15}{18}$ > $\dfrac{14}{18}$ nên $\dfrac{5}{6}$ > $\dfrac{7}{9}$}$
c, $\dfrac{5}{7}$ và $\dfrac{10}{13}$
$\text{Tử số chung : 5 × 2 = 10}$
$\text{$\dfrac{5}{7}$ = $\dfrac{5 × 2}{7 × 2}$ = $\dfrac{10}{14}$}$
$\text{$\dfrac{10}{13}$ : Giữ nguyên}$
$\text{$\dfrac{10}{14}$ < $\dfrac{10}{13}$ nên $\dfrac{5}{7}$ < $\dfrac{10}{13}$}$
Chúc bạn học tốt !
