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lộn na !!
7x - 7 - 5x - 35 = 0
2x + 28 = 0
2x = -28
x = -14
![](https://rs.olm.vn/images/avt/0.png?1311)
a) \(\frac{3x-2}{1\frac{2}{5}}=\frac{2\frac{3}{7}}{2\frac{3}{5}}\Rightarrow3x-2=1.\frac{2}{5}.\frac{2\frac{3}{7}}{2\frac{3}{5}}=\frac{7}{5}.\frac{17}{7}.\frac{5}{13}\)
\(3x-2=\frac{17}{13}\Rightarrow3x=2+\frac{17}{13}=\frac{43}{13}\Rightarrow x=\frac{43}{39}.\)
b) \(\frac{x}{0,16}=\frac{9}{x}\Rightarrow x^2=9.0,16=1,44\Rightarrow x=\pm1,2\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\begin{array}{l}a)\frac{x}{{ - 3}} = \frac{7}{{0,75}}\\ \Rightarrow x.0,75 = ( - 3).7\\ \Rightarrow x = \frac{{( - 3).7}}{{0,75}} = - 28\end{array}\)
Vậy x = 28
\(\begin{array}{l}b) - 0,52:x = \sqrt {1,96} :( - 1,5)\\ - 0,52:x = 1,4:( - 1,5)\\ x = \dfrac{(-0,52).(-1,5)}{1,4}\\x = \frac{39}{{70}}\end{array}\)
Vậy x = \(\frac{39}{{70}}\)
\(\begin{array}{l}c)x:\sqrt 5 = \sqrt 5 :x\\ \Leftrightarrow \frac{x}{{\sqrt 5 }} = \frac{{\sqrt 5 }}{x}\\ \Rightarrow x.x = \sqrt 5 .\sqrt 5 \\ \Leftrightarrow {x^2} = 5\\ \Leftrightarrow \left[ {_{x = - \sqrt 5 }^{x = \sqrt 5 }} \right.\end{array}\)
Vậy x \( \in \{ \sqrt 5 ; - \sqrt 5 \} \)
Chú ý:
Nếu \({x^2} = a(a > 0)\) thì x = \(\sqrt a \) hoặc x = -\(\sqrt a \)
a: \(\dfrac{x}{-3}=\dfrac{7}{0.75}=\dfrac{28}{3}\)
=>\(x=\dfrac{28\left(-3\right)}{3}=-28\)
b: \(-\dfrac{0.52}{x}=\dfrac{\sqrt{1.96}}{-1.5}=\dfrac{1.4}{-1.5}\)
=>\(x=0.52\cdot\dfrac{1.5}{1.4}=\dfrac{39}{70}\)
c: \(\dfrac{x}{\sqrt{5}}=\dfrac{\sqrt{5}}{x}\)
=>\(x^2=5\)
=>\(x=\pm\sqrt{5}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\text{a)}\frac{37-x}{x+13}=\frac{3}{7}\)
\(\Leftrightarrow3\left(x+13\right)=7\left(37-x\right)\)
\(\Leftrightarrow3x+39=259-7x\)
\(\Leftrightarrow3x+7x=259-39\)
\(\Leftrightarrow10x=220\)
\(\Leftrightarrow x=22\)
\(\text{b)}\frac{x+4}{20}=\frac{5}{x+4}\)
\(\Leftrightarrow\left(x+4\right)^2=100\)
\(\Leftrightarrow\orbr{\begin{cases}x+4=10\\x+4=-10\end{cases}\Leftrightarrow}\orbr{\begin{cases}x=6\\x=-14\end{cases}}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
\(\frac{x-3}{5-x}=\frac{5}{7}\)
\(\Leftrightarrow\left(x-3\right).7=5.\left(5-x\right)\)
\(\Leftrightarrow7x-21=25-5x\)
\(\Leftrightarrow7x+5x=25+21\)
\(\Leftrightarrow12x=46\)
\(\Leftrightarrow x=\frac{46}{12}=\frac{23}{6}\)
Vậy x = \(\frac{23}{6}\)
![](https://rs.olm.vn/images/avt/0.png?1311)
a, \(\frac{x-6}{x+4}=\frac{2}{7}\Rightarrow7x-42=2x+8\)ĐK : \(x\ne-4\)
\(\Leftrightarrow5x=50\Leftrightarrow x=10\)(tm)
b, \(\left(x+5\right):2\frac{1}{2}=\frac{40}{x+5}\)ĐK : \(x\ne-5\)
\(\Leftrightarrow\frac{5\left(x+5\right)}{2}=\frac{40}{x+5}\Rightarrow5\left(x+5\right)^2=80\Leftrightarrow\left(x+5\right)^2=16\)
TH1 : \(x+5=4\Leftrightarrow x=-1\)
TH2 : \(x+5=-4\Leftrightarrow x=-9\)
![](https://rs.olm.vn/images/avt/0.png?1311)
Bài 2:
a: =>x/4=1/8
hay x=1/2
b: \(\Leftrightarrow\dfrac{x}{-5}=\dfrac{11}{6}\)
hay x=-55/6
c: \(\Leftrightarrow\dfrac{-3.5}{x}=\dfrac{4.25}{8}\)
hay x=-112/17
7.(x-1)= 5.(x+5)
7.x-7. = 5.x+25
7.x -5.x =25+7
2.x. = 32
x = 32:2
x. = 16
làm rõ ràng, đầy đủ chi tiết luôn