Đáp án:
1, a, $\dfrac{13}{15}$
b, $\dfrac{77}{72}$
c, $\dfrac{46}{35}$
d, $-\dfrac{25}{27}$
2, $A=\dfrac{1}{5}$
$B=1$
Giải thích các bước giải:
1,
a, $\dfrac{1}{5}+x=-\dfrac{2}{3}\Leftrightarrow x=-\dfrac{2}{3}-\dfrac{1}{5}=\dfrac{13}{15}$
b, $-\dfrac{5}{8}+x=\dfrac{4}{9}\Leftrightarrow x=\dfrac{4}{9}+\dfrac{5}{8}=\dfrac{77}{72}$
c, $1\dfrac{3}{4}x+1\dfrac{1}{2}=-\dfrac{4}{5}\Leftrightarrow 1\dfrac{3}{4}x=-\dfrac{4}{5}-1\dfrac{1}{2}$
$\Leftrightarrow 1\dfrac{3}{4}x=-\dfrac{23}{10}\Leftrightarrow x=-\dfrac{46}{35}$
d, $x(\dfrac{1}{5}+\dfrac{1}{4})+(\dfrac{1}{7}+\dfrac{1}{8})=0\Leftrightarrow x\dfrac{9}{20}+\dfrac{15}{56}=0$
$\Leftrightarrow x=-\dfrac{15}{56}:\dfrac{9}{20}=-\dfrac{25}{27}$
2,
$A=(-0,75-\dfrac{1}{4}):(-5)+\dfrac{1}{15}-(\dfrac{-1}{5}):(-3)$
$=(-1):(-5)+\dfrac{1}{15}-\dfrac{1}{15}=\dfrac{1}{5}$
$B=(\dfrac{3}{25}-1,12):\dfrac{3}{7}:[(3\dfrac{1}{2}-3\dfrac{2}{3}):\dfrac{1}{14}]$
$=-1.\dfrac{7}{3}:(-\dfrac{1}{6}.14)=-\dfrac{7}{3}:(-\dfrac{7}{3})=1$
