Đáp án:
$1)
a) \dfrac{3}{11}\\
b)
-1\\
c)
\dfrac{-9}{10}\\
2)
a)
x=\dfrac{5}{8}\\
b)
x=\dfrac{86}{15}\\
c)
x=\dfrac{7}{4}$
Giải thích các bước giải:
$1)
a) \dfrac{2}{5}+\left ( \dfrac{3}{11}+\dfrac{-2}{5} \right )\\
=\dfrac{2}{5}+ \dfrac{3}{11}+\dfrac{-2}{5} \\
=\left ( \dfrac{2}{5}+\dfrac{-2}{5} \right )+\dfrac{3}{11}\\
=\dfrac{3}{11}\\
b)
\dfrac{-5}{7}.\dfrac{4}{13}+\dfrac{-5}{7}.\dfrac{9}{13}+\dfrac{-2}{7}\\
=\dfrac{-5}{7}.\left ( \dfrac{4}{13}+\dfrac{9}{13} \right )+\dfrac{-2}{7}\\
=\dfrac{-5}{7}.\dfrac{13}{13}+\dfrac{-2}{7}\\
=\dfrac{-7}{7}=-1\\
c)
\dfrac{-9}{10}.\dfrac{5}{14}+\dfrac{1}{10}.\dfrac{-9}{2}+\dfrac{1}{7}.\dfrac{-9}{10}\\
=\dfrac{-9}{10}.\left ( \dfrac{5}{14}+\dfrac{1}{2}+\dfrac{1}{7} \right )\\
=\dfrac{-9}{10}.\left ( \dfrac{5}{14}+\dfrac{7}{14}+\dfrac{2}{14} \right )\\
=\dfrac{-9}{10}.\dfrac{14}{14}\\
=\dfrac{-9}{10}\\
2)
a)
2x+\dfrac{1}{4}=\dfrac{3}{2}\\
\Leftrightarrow 2x=\dfrac{3}{2}-\dfrac{1}{4}\\
\Leftrightarrow 2x=\dfrac{6}{4}-\dfrac{1}{4}\\
\Leftrightarrow 2x=\dfrac{5}{4}\\
\Leftrightarrow x=\dfrac{5}{8}\\
b)
(x-5)-\dfrac{1}{3}=\dfrac{2}{5}\\
\Leftrightarrow x-5=\dfrac{2}{5}+\dfrac{1}{3}\\
\Leftrightarrow x-5=\dfrac{6}{15}+\dfrac{5}{15}\\
\Leftrightarrow x-5=\dfrac{11}{15}\\
\Leftrightarrow x=\dfrac{11}{15}+5\\
\Leftrightarrow x=\dfrac{11}{15}+\dfrac{15.5}{15}\\
\Leftrightarrow x=\dfrac{86}{15}\\
c)
\left (4,5-2x \right ):\dfrac{3}{4}=1\dfrac{1}{3}\\
\Leftrightarrow 4,5-2x=\dfrac{4}{3}.\dfrac{3}{4}\\
\Leftrightarrow 2x=4,5-1=3,5\\
\Leftrightarrow 2x=\dfrac{7}{2}\\
\Leftrightarrow x=\dfrac{7}{4}$
