Bài 3:\(a,x+\dfrac{1}{4}=\dfrac{4}{3}\\ =>x=\dfrac{4}{3}-\dfrac{1}{4}\\ =>x=\dfrac{13}{12}\\ b,\dfrac{3}{4}+\dfrac{2}{5}x=\dfrac{29}{60}\\ \Leftrightarrow\dfrac{2}{5}x=\dfrac{29}{60}-\dfrac{3}{4}=-\dfrac{4}{15}\\ \Leftrightarrow x=-\dfrac{4}{15}:\dfrac{2}{5}\\ \Leftrightarrow x=-\dfrac{2}{3}\\ c,1\dfrac{3}{4}x+1\dfrac{1}{2}=-\dfrac{4}{5}\\ \Leftrightarrow\dfrac{7}{4}x+\dfrac{3}{2}=\dfrac{-4}{5}\\ \Leftrightarrow\dfrac{7}{4}x=\dfrac{-4}{5}-\dfrac{3}{2}=-\dfrac{23}{10}\\ \Leftrightarrow x=\dfrac{-23}{10}:\dfrac{7}{4}=\dfrac{-46}{35}\\ d,\dfrac{11}{12}-\left(\dfrac{2}{5}+x\right)=\dfrac{2}{3}\\ \Leftrightarrow\dfrac{2}{5}+x=\dfrac{11}{12}-\dfrac{2}{3}=\dfrac{1}{4}\\ \Leftrightarrow x=\dfrac{1}{4}-\dfrac{2}{5}\\ \Leftrightarrow x=-\dfrac{3}{20}\)
Bài `4`
\(a,2\dfrac{3}{4}x=3\dfrac{1}{7}:0,01\)
\(\dfrac{11}{4}x=\dfrac{22}{7}:\dfrac{1}{100}\)
\(\dfrac{11}{4}x=\dfrac{2200}{7}\)
\(x=\dfrac{2200}{7}:\dfrac{11}{4}\)
\(x=\dfrac{800}{7}\)
Vậy ` x = 800/7`
\(b,2.x.\left(x-\dfrac{1}{7}\right)=0\)
\(\Rightarrow\left[{}\begin{matrix}2.x=0\\x-\dfrac{1}{7}=0\end{matrix}\right.\)\(\Rightarrow\left[{}\begin{matrix}x=0\\x=\dfrac{1}{7}\end{matrix}\right.\)
Vậy \(\in\) \(\left\{0;\dfrac{1}{7}\right\}\)
\(c,\dfrac{3}{4}+\dfrac{1}{4}:x=\dfrac{2}{5}\)
\(\dfrac{1}{4}:x=\dfrac{2}{5}-\dfrac{3}{4}\)
\(\dfrac{1}{4}:x=-\dfrac{7}{20}\)
\(x=\dfrac{1}{4}:-\dfrac{7}{20}\)
\(x=-\dfrac{5}{7}\)
Vậy `x = -5/7`
\(d,3,8:2x=\dfrac{1}{4}:2\dfrac{2}{3}\)
\(\dfrac{19}{5}:2x=\dfrac{1}{4}:\dfrac{8}{3}\)
\(2x=\dfrac{19}{5}:\dfrac{1}{4}:\dfrac{8}{3}\)
\(2x=\dfrac{57}{10}\)
\(x=\dfrac{57}{10}:2\)
\(x=\dfrac{57}{20}\)
Vậy `x = 57/20`
Sửa câu d:
\(d,3,8:2x=\dfrac{1}{4}:2\dfrac{2}{3}\)
\(\dfrac{19}{10}x=\dfrac{3}{32}\)
\(x=\dfrac{3}{32}:\dfrac{19}{10}\)
\(x=\dfrac{15}{304}\)
Vậy ` x = 15/304`
