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Vì x và y là hai đại lượng tỉ lệ thuận nên x 1 x 2 = y 1 y 2
Suy ra x 1 − 6 = y 1 3 = 3 x 1 − 18 = 2 y 1 6 = 3 x 1 + 2 y 1 − 18 + 6 = 24 − 12 = − 2
Nên x 1 = ( − 2 ) . ( − 6 ) = 12 ; y 1 = ( − 2 ) .3 = − 6
Đáp án cần chọn là C
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a.
\(\frac{x-1}{x-5}=\frac{6}{7}\)
\(\left(x-1\right)\times7=6\times\left(x-5\right)\)
\(7x-7=6x-30\)
\(7x-6x=-30+7\)
\(x=-23\)
b.
\(\frac{x^2}{6}=\frac{24}{25}\)
\(x^2=\frac{24}{25}\times6\)
\(x^2=\frac{144}{25}\)
\(x^2=\left(\pm\frac{12}{5}\right)^2\)
\(x=\pm\frac{12}{5}\)
Vậy \(x=\frac{12}{5}\) hoặc \(x=-\frac{12}{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{35}{x}=\frac{15}{12}\Leftrightarrow x=35.12:15=28\)
\(-\frac{2,6}{x}=-\frac{12}{42}\Leftrightarrow\frac{-2,6}{x}=-\frac{2}{7}\Leftrightarrow x=-2,6.7:\left(-2\right)=\frac{91}{10}\)
\(\frac{125}{10}=\frac{x}{45}\Leftrightarrow x=125.45:10=562,5\)
\(\frac{x^2}{6}=\frac{24}{25}\Leftrightarrow x^2=6.24:25=\frac{144}{25}\Leftrightarrow x=\sqrt{\frac{144}{25}}\Leftrightarrow x=\frac{12}{5}\)
1; \(\dfrac{35}{x}\) = \(\dfrac{15}{12}\) (\(x\ne\) 0)
⇒ \(x\) = 35 : \(\dfrac{15}{12}\)
⇒ \(x\) = 28
Vậy \(x=28\)
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a) \(\frac{x}{6}^2=\frac{24}{25}\)
\(\Rightarrow x^2.25=6.24\)
\(\Rightarrow x^2.25=144\)
\(\Rightarrow x^2=144\div25\)
\(\Rightarrow x^2=5,76=2,4^2=\left(-2,4^2\right)\)
\(\Rightarrow x\in\left\{2,4;-2,4\right\}\)
Vậy \(x\in\left\{2,4;-2,4\right\}\)
b) \(\frac{72-x}{7}=\frac{x-40}{9}\)
\(\Rightarrow\left(72-x\right).9=\left(x-40\right).7\)
\(\Rightarrow648-9x=7x-280\)
\(\Rightarrow\left(-280\right)-648\) \(=-9x-7x\)
\(\Rightarrow-928=-16x\)
\(\Rightarrow x=58\)
Vậy \(x=58\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Có: (x2 - 25)2n = 242n
=> x2 - 25 = 24
=> x2 = 24 + 25 = 49
=> x = 7
![](https://rs.olm.vn/images/avt/0.png?1311)
Ta có:
\(\frac{x^2}{6}=\frac{24}{25}\Leftrightarrow x^2.25=24.6\)
\(\Leftrightarrow x^2=\frac{24.6}{25}=\frac{144}{25}=5,76\)
\(\Leftrightarrow x=\sqrt{5,76}=2,4;x=-\sqrt{5,76}=-2,4\)
Vậy \(x=2,4\) hoặc \(x=-2,4\)