$\text{Câu a}$

$\text{$\dfrac{-1}{2}$+$\dfrac{3}{5}$=$\dfrac{-5}{10}$+$\dfrac{6}{10}$=$\dfrac{1}{10}$}$

$\text{Câu b}$

$\text{$\dfrac{-4}{7}$+$\dfrac{1}{2}$=$\dfrac{-8}{14}$+$\dfrac{7}{14}$=$\dfrac{-1}{14}$}$

$\text{Câu c}$

$\text{($\dfrac{-2}{3}$)²:$\dfrac{2}{5}$-$\dfrac{1}{3}$}$

$\text{=$\dfrac{4}{9}$:$\dfrac{2}{5}$-$\dfrac{1}{3}$}$

$\text{=$\dfrac{10}{9}$-$\dfrac{1}{3}$}$

$\text{=$\dfrac{10}{9}$-$\dfrac{3}{9}$}$

$\text{=$\dfrac{7}{9}$}$

$\text{Câu d}$

$\text{($\dfrac{-1}{3}$)²:$\dfrac{2}{5}$-$\dfrac{5}{2}$}$

$\text{=$\dfrac{1}{9}$:$\dfrac{2}{5}$-$\dfrac{5}{2}$}$

$\text{=$\dfrac{5}{18}$-$\dfrac{5}{2}$}$

$\text{=$\dfrac{5}{18}$-$\dfrac{45}{18}$}$

$\text{=$\dfrac{-40}{18}$}$

$\text{=$\dfrac{-20}{9}$}$

Bài 1  :

a. $\frac{-1}{2}$ +$\frac{3}{5}$ = $\frac{-5}{10}$ +$\frac{6}{10}$ =$\frac{1}{10}$ 

b.$\frac{-4}{7}$ + $\frac{1}{2}$ = $\frac{-8}{14}$ +$\frac{7}{14}$ =$\frac{-1}{14}$ 

c.($\frac{-2}{3}$) $^{2}$ : $\frac{2}{5}$-$\frac{1}{3}$ = $\frac{4}{9}$x $\frac{5}{2}$-$\frac{1}{3}$=$\frac{10}{9}$ -$\frac{1}{3}$ = $\frac{7}{9}$ 

d.(-$\frac{1}{3}$)$^{2}$ : $\frac{2}{5}$ -$\frac{5}{2}$ = $\frac{1}{9}$ x $\frac{5}{2}$-$\frac{5}{2}$=$\frac{5}{18}$ -$\frac{5}{2}$ =$\frac{-20}{9}$ 

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