Bài 1:
a) $\dfrac{4}{7}.\dfrac{5}{11}+\dfrac{4}{7}.\dfrac{6}{11}$
$=\dfrac{4}{7}.(\dfrac{5}{11}+\dfrac{6}{11})$
$=\dfrac{4}{7}.1$
$=\dfrac{4}{7}$
b) $-5\dfrac{1}{7}+5\dfrac{2}{5}$
$=-5+\dfrac{1}{7}+5+\dfrac{2}{5}$
$=\dfrac{1}{7}+\dfrac{2}{5}$
$=\dfrac{19}{35}$
c) $\dfrac{4}{7}.(\dfrac{2}{5}.\dfrac{4}{7})$
$=\dfrac{4}{7}.\dfrac{2.4}{5.7}$
$=\dfrac{4}{7}.\dfrac{8}{35}$
$=\dfrac{32}{245}$
d) $\dfrac{4}{9}:\dfrac{-1}{7}+6\dfrac{5}{9}:\dfrac{-1}{7}$
$=\dfrac{4}{9}.(-7)+\dfrac{59}{9}.(-7)$
$=(-7).(\dfrac{4}{9}+\dfrac{59}{9})$
$=(-7).7$
$=-49$
Bài 2:
a) $\dfrac{4}{5}x=\dfrac{8}{35}$
$x=\dfrac{8}{35}:\dfrac{4}{5}$
$x=\dfrac{8}{35}.\dfrac{5}{4}$
$x=\dfrac{2}{7}$
Vậy $x=\dfrac{2}{7}$
b) $x+\dfrac{3}{2}=1\dfrac{1}{4}:\dfrac{1}{4}$
$x+\dfrac{3}{2}=\dfrac{5}{4}.4$
$x+\dfrac{3}{2}=5$
$x=5-\dfrac{3}{2}$
$x=\dfrac{7}{2}$
Vậy $x=\dfrac{7}{2}$
c) $\dfrac{-11}{14}-x=\dfrac{-3}{4}$
$x=\dfrac{-11}{14}-\dfrac{-3}{4}$
$x=\dfrac{-1}{28}$
Vậy $x=\dfrac{-1}{28}$
d) $\dfrac{x}{4}=\dfrac{9}{x}$
$x^2=9.4$
$x^2=36$
$x^2=6^2$ hoặc $x^2=(-6)^2$
$x=6$ hoặc $x=-6$
Vậy $x\in\{6;-6\}$
