\(g,\left[\dfrac{3}{5}+\left(\dfrac{-1}{4}\right)\right]:\dfrac{3}{7}+\left[\left(\dfrac{-3}{4}\right)+\dfrac{2}{5}\right]:\dfrac{3}{7}\)
\(=\left\{\left[\dfrac{3}{5}+\left(\dfrac{-1}{4}\right)\right]+\left[\left(\dfrac{-3}{4}\right)+\dfrac{2}{5}\right]\right\}:\dfrac{3}{7}\)
\(=\left\{\dfrac{3}{5}-\dfrac{1}{4}-\dfrac{3}{4}+\dfrac{2}{5}\right\}:\dfrac{3}{7}\)
\(=\left\{\left(\dfrac{3}{5}+\dfrac{2}{5}\right)-\left(\dfrac{1}{4}+\dfrac{3}{4}\right)\right\}:\dfrac{3}{7}\)
\(=\left\{1-1\right\}:\dfrac{3}{7}\)
\(=0:\dfrac{3}{7}\)
\(=0\)
\(h,\dfrac{7}{8}:\left(\dfrac{2}{9}-\dfrac{1}{18}\right)+\dfrac{7}{8}:\left(\dfrac{1}{36}-\dfrac{5}{12}\right)\)
\(=\dfrac{7}{8}:\left[\left(\dfrac{2}{9}-\dfrac{1}{18}\right)+\left(\dfrac{1}{36}-\dfrac{5}{12}\right)\right]\)
\(=\dfrac{7}{8}:\left[\dfrac{1}{6}+-\dfrac{7}{18}\right]\)
\(=\dfrac{7}{8}:-\dfrac{2}{9}\)
\(=-\dfrac{63}{16}\)
Bài 18:
g: \(\left[\left(\dfrac{3}{5}+\dfrac{-1}{4}\right)\right]:\dfrac{3}{7}+\left[-\dfrac{3}{4}+\dfrac{2}{5}\right]:\dfrac{3}{7}\)
\(=\left(\dfrac{3}{5}+\dfrac{-1}{4}-\dfrac{3}{4}+\dfrac{2}{5}\right):\dfrac{3}{7}\)
\(=\left(1-1\right):\dfrac{3}{7}\)
=0
h: \(\dfrac{7}{8}:\left(\dfrac{2}{9}-\dfrac{1}{18}\right)+\dfrac{7}{8}:\left(\dfrac{1}{36}-\dfrac{5}{12}\right)\)
\(=\dfrac{7}{8}:\left(\dfrac{4}{18}-\dfrac{1}{18}\right)+\dfrac{7}{8}:\left(\dfrac{1}{36}-\dfrac{15}{36}\right)\)
\(=\dfrac{7}{8}\cdot\dfrac{18}{3}+\dfrac{7}{8}:\dfrac{-14}{36}\)
\(=\dfrac{7}{8}\cdot6+\dfrac{7}{8}\cdot\dfrac{-36}{14}\)
\(=\dfrac{7}{8}\left(6-\dfrac{36}{14}\right)=\dfrac{7}{8}\cdot\left(\dfrac{84}{14}-\dfrac{36}{14}\right)\)
\(=\dfrac{7}{8}\cdot\dfrac{48}{14}=\dfrac{7}{14}\cdot\dfrac{48}{8}=\dfrac{6}{2}=3\)
Bài 19:
a: \(\dfrac{2}{5}\cdot x=\dfrac{4}{5}\)
=>\(x=\dfrac{4}{5}:\dfrac{2}{5}=\dfrac{4}{5}\cdot\dfrac{5}{2}=\dfrac{20}{10}=2\)
b: \(\dfrac{1}{10}:x=\dfrac{2}{4}\)
=>\(x=\dfrac{1}{10}:\dfrac{1}{2}=\dfrac{1}{10}\cdot2=\dfrac{2}{10}=\dfrac{1}{5}\)
c: \(x:\dfrac{2}{3}=\dfrac{3}{2}\)
=>\(x=\dfrac{3}{2}\cdot\dfrac{2}{3}=\dfrac{6}{6}=1\)
d: \(\dfrac{4}{11}x-\dfrac{1}{3}=\dfrac{2}{5}\)
=>\(\dfrac{4}{11}x=\dfrac{2}{5}+\dfrac{1}{3}=\dfrac{6}{15}+\dfrac{5}{15}=\dfrac{11}{15}\)
=>\(x=\dfrac{11}{15}:\dfrac{4}{11}=\dfrac{11}{15}\cdot\dfrac{11}{4}=\dfrac{121}{60}\)
e: \(\dfrac{1}{4}+\dfrac{-4}{3}x=-\dfrac{7}{5}\)
=>\(-\dfrac{4}{3}x=-\dfrac{7}{5}-\dfrac{1}{4}=-\dfrac{28}{20}-\dfrac{5}{20}=-\dfrac{33}{20}\)
=>\(x=\dfrac{33}{20}:\dfrac{4}{3}=\dfrac{33}{20}\cdot\dfrac{3}{4}=\dfrac{99}{80}\)
f: \(-\dfrac{6}{7}-\dfrac{1}{5}x=-4\)
=>\(\dfrac{1}{5}x+\dfrac{6}{7}=4\)
=>\(\dfrac{1}{5}x=4-\dfrac{6}{7}=\dfrac{28}{7}-\dfrac{6}{7}=\dfrac{22}{7}\)
=>\(x=\dfrac{22}{7}:\dfrac{1}{5}=\dfrac{22}{7}\cdot5=\dfrac{110}{7}\)
g: \(\dfrac{1}{2}+\dfrac{2}{3}x=-\dfrac{5}{4}\)
=>\(\dfrac{2}{3}x=-\dfrac{5}{4}-\dfrac{1}{2}=-\dfrac{7}{4}\)
=>\(x=-\dfrac{7}{4}:\dfrac{2}{3}=-\dfrac{7}{4}\cdot\dfrac{3}{2}=-\dfrac{21}{8}\)
h: \(-\dfrac{3}{4}-\dfrac{5}{7}x=\dfrac{3}{5}\)
=>\(\dfrac{5}{7}x=-\dfrac{3}{4}-\dfrac{3}{5}=-\dfrac{15}{20}-\dfrac{12}{20}=\dfrac{-27}{20}\)
=>\(x=-\dfrac{27}{20}:\dfrac{5}{7}=-\dfrac{27}{20}\cdot\dfrac{7}{5}=\dfrac{-189}{100}\)
i: \(-\dfrac{5}{2}+x:7=\dfrac{1}{3}\)
=>\(x:7=\dfrac{1}{3}+\dfrac{5}{2}=\dfrac{2}{6}+\dfrac{15}{6}=\dfrac{17}{6}\)
=>\(x=\dfrac{17}{6}\cdot7=\dfrac{119}{6}\)
\(a,\dfrac{2}{5}\cdot x=\dfrac{4}{5}\)
\(\Rightarrow x=\dfrac{4}{5}:\dfrac{2}{5}\)
\(\Rightarrow x=2\)
Vậy `x = 2`
\(b,\dfrac{1}{10}\cdot x=\dfrac{2}{4}\)
\(\Rightarrow x=\dfrac{2}{4}:\dfrac{1}{10}\)
\(\Rightarrow x=5\)
Vậy `x = 5`
\(c,x:\dfrac{2}{3}=\dfrac{3}{2}\)
\(\Rightarrow x=\dfrac{3}{2}\cdot\dfrac{2}{3}\)
\(\Rightarrow x=1\)
Vậy `x = 1`
\(d,\dfrac{4}{11}x-\dfrac{1}{3}=\dfrac{2}{5}\)
\(\Rightarrow\dfrac{4}{11}x=\dfrac{2}{5}+\dfrac{1}{3}\)
\(\Rightarrow\dfrac{4}{11}x=\dfrac{11}{15}\)
\(\Rightarrow x=\dfrac{11}{15}:\dfrac{4}{11}\)
\(\Rightarrow x=\dfrac{121}{60}\)
Vậy `x = 121/60`
\(e,\dfrac{1}{4}+\dfrac{-4}{3}\cdot x=\dfrac{-7}{5}\)
\(\Rightarrow\dfrac{-4}{3}\cdot x=\dfrac{-7}{5}-\dfrac{1}{4}\)
\(\Rightarrow\dfrac{-4}{3}\cdot x=-\dfrac{33}{20}\)
\(\Rightarrow x=-\dfrac{33}{20}:\dfrac{-4}{3}\)
\(\Rightarrow x=\dfrac{99}{80}\)
Vậy \(x=\dfrac{99}{80}\)
\(f,\dfrac{-6}{7}-\dfrac{1}{5}x=-4\)
\(\Rightarrow\dfrac{1}{5}x=\dfrac{-6}{7}--4\)
\(\Rightarrow\dfrac{1}{5}x=\dfrac{-6}{7}+4\)
\(\Rightarrow\dfrac{1}{5}x=\dfrac{22}{7}\)
\(\Rightarrow x=\dfrac{22}{7}:\dfrac{1}{5}\)
\(\Rightarrow x=\dfrac{110}{7}\)
Vậy `x = 110/7`
\(g,\dfrac{1}{2}+\dfrac{2}{3}\cdot x=\dfrac{-5}{4}\)
\(\Rightarrow\dfrac{2}{3}\cdot x=\dfrac{-5}{4}-\dfrac{1}{2}\)
\(\Rightarrow\dfrac{2}{3}\cdot x=-\dfrac{7}{4}\)
\(\Rightarrow x=-\dfrac{7}{4}:\dfrac{2}{3}\)
\(\Rightarrow x=-\dfrac{21}{8}\)
Vậy `x = -21/8`
\(h,\left(\dfrac{-3}{4}\right)-\dfrac{5}{7}x=\dfrac{3}{5}\)
\(\Rightarrow\dfrac{5}{7}x=\left(\dfrac{-3}{4}\right)-\dfrac{3}{5}\)
\(\Rightarrow\dfrac{5}{7}x=-\dfrac{27}{20}\)
\(\Rightarrow x=-\dfrac{27}{20}:\dfrac{5}{7}\)
\(\Rightarrow x=-\dfrac{189}{100}\)
Vậy `x = -189/100`
\(i,\dfrac{-5}{2}+x:7=\dfrac{1}{3}\)
\(\Rightarrow x:7=\dfrac{1}{3}-\dfrac{-5}{2}\)
\(\Rightarrow x:7=\dfrac{1}{3}+\dfrac{5}{2}\)
\(\Rightarrow x:7=\dfrac{17}{6}\)
\(\Rightarrow x=\dfrac{17}{6}\cdot7\)
\(\Rightarrow x=\dfrac{119}{6}\)
Vậy `x = 119/6`
