Tìm số hữu tỉ $x$ trong các tỉ lệ thức sau:
a) $\dfrac{x}{6}=\dfrac{-3}{4}$;
b) $\dfrac{5}{x}=\dfrac{15}{-20}$;
c) $\dfrac{x+11}{14-x}=\dfrac{2}{3}$.
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a; 5\(x\) - 7 = 3\(x\) + 9
5\(x\) - 3\(x\) = 9 + 7
2\(x\) = 16
\(x\) = 16: 2
\(x\) = 8
Vậy \(x=8\)
b; 1\(\dfrac{3}{4}\)\(x\) + 1\(\dfrac{1}{2}\) = - \(\dfrac{4}{5}\)
\(\dfrac{7}{4}\)\(x\) + \(\dfrac{3}{2}\) = - \(\dfrac{4}{5}\)
\(\dfrac{7}{4}\)\(x\) = - \(\dfrac{4}{5}\) - \(\dfrac{3}{2}\)
\(\dfrac{7}{4}\)\(x\) = - \(\dfrac{23}{10}\)
\(x\) = - \(\dfrac{23}{10}\) : \(\dfrac{7}{4}\)
\(x\) = - \(\dfrac{46}{35}\)
Vậy \(x=-\dfrac{46}{35}\)
c; \(x\) + \(\dfrac{1}{2}\) = 25:23
\(x\) + \(\dfrac{1}{2}\) = 22
\(x\) + \(\dfrac{1}{2}\) = 4
\(x\) = 4 - \(\dfrac{1}{2}\)
\(x\) = \(\dfrac{7}{2}\)
Vậy \(x=\dfrac{7}{2}\)
d; (\(x+\dfrac{1}{2}\))2 = \(\dfrac{4}{25}\)
\(\left[{}\begin{matrix}x+\dfrac{1}{2}=-\dfrac{2}{5}\\x+\dfrac{1}{2}=\dfrac{2}{5}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-\dfrac{2}{5}-\dfrac{1}{2}\\x=-\dfrac{2}{5}+\dfrac{1}{2}\end{matrix}\right.\)
\(\left[{}\begin{matrix}x=-\dfrac{9}{10}\\x=-\dfrac{1}{10}\end{matrix}\right.\)
vậy \(x\) \(\in\) {- \(\dfrac{9}{10}\); - \(\dfrac{1}{10}\)}
2.(\(\dfrac{1}{4}\) - 3\(x\)) = \(\dfrac{1}{5}\) - 4\(x\)
\(\dfrac{1}{2}\) - 6\(x\) = \(\dfrac{1}{5}\) - 4\(x\)
- 4\(x\) + 6\(x\) =\(\dfrac{1}{2}\) - \(\dfrac{1}{5}\)
2\(x\) = \(\dfrac{3}{10}\)
\(x\) = \(\dfrac{3}{10}\): 2
\(x=\dfrac{3}{20}\)
Vậy \(x=\dfrac{3}{20}\)
Ta có:
\(y=2x\)
\(x=\dfrac{1}{3}z\)
\(\Rightarrow y=2\left(\dfrac{1}{3}z\right)\)
\(\Rightarrow y=\dfrac{2}{3}z\)
Vậy y tỉ lệ thuận với z theo hệ số tỉ lệ \(\dfrac{2}{3}\).
a; \(\dfrac{x}{6}\) = \(\dfrac{-3}{4}\)
\(x=\dfrac{-3}{4}.6\)
\(x\) = - \(\dfrac{9}{2}\)
Vậy \(x=-\dfrac{9}{2}\)
b; \(\dfrac{5}{x}\) = \(\dfrac{15}{-20}\) (đk \(x\ne0\))
\(x\) = 5 : \(\dfrac{15}{-20}\)
\(x=-\dfrac{20}{3}\)
Vậy \(x=-\dfrac{20}{3}\)
c; \(\dfrac{x+11}{14-x}\) = \(\dfrac{2}{3}\) (đk \(x\ne14\))
3.(\(x+11\)) = 2.(14 - \(x\))
3\(x\) + 33 = 28 - 2\(x\)
3\(x\) + 2\(x\) = 28 - 33
5\(x\) = -5
\(x\) = -1
Vậy \(x\) = -1