Câu 1:
a, $\frac{-13}{14}$ + $\frac{3}{7}$
= $\frac{-13 + 6}{14}$
= $\frac{-7}{14}$
= $\frac{-1}{2}$
b, $\frac{-9}{10}$ + 0,9 . ($\frac{1}{5}$ - $\frac{1}{6}$) : 20%
= $\frac{-9}{10}$ + $\frac{9}{10}$ . ($\frac{6 - 5}{30}$) : $\frac{1}{5}$
= $\frac{-9}{10}$ + $\frac{9}{10}$ . $\frac{1}{30}$ . 5
= $\frac{-9}{10}$ + $\frac{3}{100}$ . 5
= $\frac{-9}{10}$ + $\frac{3}{20}$
= $\frac{-18 + 3}{20}$
= $\frac{-15}{20}$
= $\frac{-3}{4}$
c, $\frac{-2}{9}$ . $\frac{5}{19}$ + $\frac{14}{9}$ . $\frac{-2}{9}$ + 24$\frac{2}{9}$
= $\frac{-2}{9}$ . ($\frac{5}{19}$ + $\frac{14}{9}$) + 24$\frac{2}{9}$
= $\frac{-2}{9}$ . 1 + 24$\frac{2}{9}$
= $\frac{-2}{9}$ + 24$\frac{2}{9}$
= 24
Câu 2:
a, x - $\frac{3}{4}$ = $\frac{-11}{12}$
x = $\frac{-11}{12}$ + $\frac{3}{4}$
x = $\frac{-11 + 9}{12}$
x = $\frac{-2}{12}$
x = $\frac{-1}{6}$
b, $\frac{1}{3}$ + $\frac{2}{3}$ : x = 2$\frac{1}{3}$
$\frac{1}{3}$ + $\frac{2}{3}$ : x = $\frac{7}{3}$
$\frac{2}{3}$ : x = $\frac{7}{3}$ - $\frac{1}{3}$
$\frac{2}{3}$ : x = $\frac{6}{3}$
$\frac{2}{3}$ : x = 2
x = $\frac{2}{3}$ : 2
x = $\frac{2}{3}$ . $\frac{1}{2}$
x = $\frac{1}{3}$
c, $\frac{1}{2}$x + $\frac{1}{4}$x = $\frac{-3}{8}$
x ($\frac{1}{2}$ + $\frac{1}{4}$) = $\frac{-3}{8}$
x ($\frac{2 + 1}{4}$) = $\frac{-3}{8}$
x . $\frac{3}{4}$ = $\frac{-3}{8}$
x = $\frac{-3}{8}$ : $\frac{3}{4}$
x = $\frac{-3}{8}$ . $\frac{4}{3}$
x = $\frac{-1}{2}$
d, |5x - 9| + 2018 = 2019
|5x - 9| = 2019 - 2018
|5x - 9| = 1
⇒\(\left[ \begin{array}{l}5x - 9 = 1\\5x - 9 = -1\end{array} \right.\)
⇒\(\left[ \begin{array}{l}5x = 1 + 9 = 10\\5x = -1 + 9 = 8\end{array} \right.\)
⇒\(\left[ \begin{array}{l}x = 10 : 5 = 2\\ x = 8 : 5 = \frac{8}{5} \end{array} \right.\)
Chúc bạn học tốt ^^
