Giải câu 1 trang 14 toán VNEN 7 tập 1 .
a) $\frac{5}{4}$.$\frac{-12}{7}$ = $\frac{5.(-12)}{4.7}$ = $\frac{5.(-3)}{7}$ = $\frac{-15}{7}$;
b) $\frac{-4}{3}$:$\frac{13}{9}$ = $\frac{-4}{3}$ . $\frac{9}{13}$ = $\frac{(-4).9}{3.13}$ = $\frac{(-4).3}{13}$ = $\frac{-12}{13}$;
c) $\frac{-5}{7}$. $\frac{49}{3}$: $\frac{7}{-6}$ = $\frac{(-5).49.(-6)}{7.3.7}$ = 10;
d) (-$\frac{9}{25}$):6 = $\frac{-9}{25}$. $\frac{1}{6}$ = $\frac{(-9).1}{25.6}$ = $\frac{-3}{50}$.