Đáp án:
$1)
a)\dfrac{-1}{3}\\
b) \dfrac{5}{17}\\
c) 15\\
2)
a)x=\dfrac{1}{8}\\
b)x=-1\\
c)
x=\dfrac{1}{16}$
Giải thích các bước giải:
$1)
a)\left ( \dfrac{2}{3}-\dfrac{8}{9} \right ):\dfrac{2}{3}\\
=\left ( \dfrac{6}{9}-\dfrac{8}{9} \right ):\dfrac{2}{3}\\
=\dfrac{-2}{9}.\dfrac{3}{2}=\dfrac{-1}{3}\\
b) \dfrac{4}{-13}+0,75-\dfrac{9}{13}-\dfrac{1}{-4}+\dfrac{5}{17}\\
=\dfrac{-4}{13}+\dfrac{3}{4}-\dfrac{9}{13}+\dfrac{1}{4}+\dfrac{5}{17}\\
=\left ( \dfrac{-4}{13}-\dfrac{9}{13}\right )+\left ( \dfrac{3}{4}+\dfrac{1}{4} \right )+\dfrac{5}{17}\\
=\dfrac{-13}{13}+\dfrac{4}{4}+\dfrac{5}{17}\\
=-1+1+\dfrac{5}{17}=\dfrac{5}{17}\\
c) \dfrac{15}{22}.9\dfrac{3}{4}+\dfrac{15}{22}.12\dfrac{1}{4}\\
=\dfrac{15}{22}.\left ( 9\dfrac{3}{4}+12\dfrac{1}{4} \right )\\
=\dfrac{15}{22}.\left ( (9+12)+(\dfrac{3}{4}+\dfrac{1}{4}) \right )\\
=\dfrac{15}{22}.\left ( 21+1\right )\\
=15\\
2)
a)\dfrac{5}{8}+x=\dfrac{3}{4}\\
\Leftrightarrow x=\dfrac{3}{4}-\dfrac{5}{8}\\
\Leftrightarrow x=\dfrac{6}{8}-\dfrac{5}{8}\\
\Leftrightarrow x=\dfrac{1}{8}\\
b)\dfrac{3}{4}-\dfrac{7}{12}:x=\dfrac{4}{3}\\
\Leftrightarrow \dfrac{7}{12}:x=\dfrac{3}{4}-\dfrac{4}{3}\\
\Leftrightarrow \dfrac{7}{12}.\dfrac{1}{x}=\dfrac{9}{12}-\dfrac{16}{12}\\
\Leftrightarrow \dfrac{7}{12}.\dfrac{1}{x}=\dfrac{-7}{12}\\
\Leftrightarrow \dfrac{1}{x}=\dfrac{-7}{12}.\dfrac{12}{7}=-1\\
\Leftrightarrow x=-1\\
c)
4\dfrac{3}{8}.x+7\dfrac{15}{24}=0,75\\
\Leftrightarrow \left ( 4\dfrac{3}{8}+7\dfrac{15}{24} \right )x=\dfrac{3}{4}\\
\Leftrightarrow \left ( (4+7)+(\dfrac{3}{8}+\dfrac{15}{24}) \right )x=\dfrac{3}{4}\\
\Leftrightarrow \left ( 11+(\dfrac{9}{24}+\dfrac{15}{24}) \right )x=\dfrac{3}{4}\\
\Leftrightarrow \left ( 11+1 \right )x=\dfrac{3}{4}\\
\Leftrightarrow x=\dfrac{3}{4}.\dfrac{1}{12}=\dfrac{1}{16}$
