Tính:

a) $\frac{3}{7}$ + (-$\frac{5}{2}$) + (-$\frac{3}{5}$)

= $\frac{3}{7}$ - $\frac{5}{2}$ - $\frac{3}{5}$

= $\frac{30}{70}$ - $\frac{175}{70}$ - $\frac{42}{70}$

= $\frac{30-175-42}{70}$

= -$\frac{187}{70}$

b) (-$\frac{4}{3}$) + (-$\frac{2}{5}$) + (-$\frac{3}{2}$)

= -$\frac{4}{3}$ - $\frac{2}{5}$ - $\frac{3}{2}$

= -$\frac{40}{30}$ - $\frac{12}{30}$ - $\frac{45}{30}$

= $\frac{-40-12-45}{30}$ 

= -$\frac{97}{30}$

c) $\frac{4}{5}$ - (-$\frac{2}{7}$) - $\frac{7}{10}$

= $\frac{4}{5}$ + $\frac{2}{7}$ - $\frac{7}{10}$

= $\frac{56}{70}$ + $\frac{20}{70}$ - $\frac{49}{70}$

= $\frac{56+20-49}{70}$

= $\frac{27}{70}$

d) $\frac{2}{3}$ - [(-$\frac{7}{4}$) - ($\frac{1}{2}$ + $\frac{3}{8}$)]

= $\frac{2}{3}$ - [(-$\frac{7}{4}$ - ($\frac{4}{8}$ + $\frac{3}{8}$)]

= $\frac{2}{3}$ - (-$\frac{7}{4}$ - $\frac{7}{8}$)

= $\frac{2}{3}$ - (-$\frac{14}{8}$ - $\frac{7}{8}$)

= $\frac{2}{3}$ - $\frac{-21}{8}$

= $\frac{16}{24}$ - $\frac{-63}{24}$

= -$\frac{79}{24}$

Đáp án:

2) d. \(x = \dfrac{5}{{21}}\)

Giải thích các bước giải:

\(\begin{array}{l}
1)a.\dfrac{3}{7} - \left( {\dfrac{5}{2} + \dfrac{3}{5}} \right)\\
 = \dfrac{3}{7} - \dfrac{{31}}{{10}} =  - \dfrac{{187}}{{70}}\\
b. - \dfrac{4}{3} - \dfrac{2}{5} - \dfrac{3}{2}\\
 =  - \dfrac{{26}}{{15}} - \dfrac{3}{2} =  - \dfrac{{97}}{{30}}\\
c.\dfrac{4}{5} + \dfrac{2}{7} - \dfrac{7}{{10}} = \dfrac{{38}}{{35}} - \dfrac{7}{{10}}\\
 = \dfrac{{27}}{{70}}\\
d.\dfrac{2}{3} - \left( { - \dfrac{7}{4} - \dfrac{7}{8}} \right)\\
 = \dfrac{2}{3} - \left( { - \dfrac{{21}}{8}} \right)\\
 = \dfrac{2}{3} + \dfrac{{21}}{8} = \dfrac{{79}}{{24}}\\
2)a.x = \dfrac{3}{4} - \dfrac{1}{3}\\
 \to x = \dfrac{5}{{12}}\\
b.x = \dfrac{5}{7} + \dfrac{2}{5}\\
 \to x = \dfrac{{39}}{{35}}\\
c.x = \dfrac{6}{7} - \dfrac{2}{3}\\
 \to x = \dfrac{4}{{21}}\\
d.x = \dfrac{4}{7} - \dfrac{1}{3}\\
 \to x = \dfrac{5}{{21}}
\end{array}\)