Câu a bạn Mạnhlàm đúng rồi vậy mik làm câu b nhé

<br class="Apple-interchange-newline"><div id="inner-editor"></div>72−x7=x−709

<=>(72−x).963=(x−70).763

=>648−9x−7x+49063=0

<=>.−16x+113863=0

<=>-16x+1138=0

<=>x=71,125

a) theo đề bài ta có: x.x=0,16.9

=> x²=1,44

=> x²=a) theo đề bài ta có: x.x=0,16.9

=> x²=1,44

=> x²=(1,2)²

vậy x = 1,2

a) x:0,16=9:x                               b) 72-x/7=x-70/9

  => x.x=0,16.9                                 => 72+70/9=x+x/7

  => x²=1,44                                     => 718/9=x+x/7                           

  => x=1,2                                        => 718/9=x/1+x/7      

                                                       => 718/9=x.(1/1+1/7)

                                                       => 718/9=8/7x

                                                       => x=718/9: 8/7

                                                       => x= 2513/36

\(\frac{-12}{x}=\frac{4}{13}\)

\(\Rightarrow4x=13.\left(-12\right)=-156\)

\(\Rightarrow x=-156:4=-39\)

\(\frac{-15}{72}=\frac{125}{-3y}\)

\(\Rightarrow\frac{-15}{72}=\frac{-3000}{72y}\)

\(\Rightarrow-15y=-3000\)

\(\Rightarrow y=-3000:-15=200\)

\(\frac{49}{21}=\frac{-14z}{-7}\)

\(\Rightarrow\frac{49}{21}=\frac{42z}{21}\)

\(\Rightarrow49=42z\)

\(\Rightarrow z=\frac{49}{42}\)

x=-39 

y=200

z=1,167

x= -12 x 13 : 4 = -39

y= 125 x 72 : (-15) = 600

z= ... mình không biết

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) \(\frac{x}{0,16}=\frac{9}{x}\Rightarrow x^2=9.0,16=1,44\Rightarrow x=\pm1,2\)

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 : \(x+5=-4\Leftrightarrow x=-9\)

a/ x:0,16 = 9:x hay \(\frac{x}{0,16}=\frac{9}{x}\)

=>x.x=0,16.9

=>x²=1,44

=>x²=(1,2)²

=>x=1,2 hoặc x=-1,2

b)\(\frac{72-x}{7}=\frac{x-10}{9}\)

=>(72-x).9=7.(x-10)

648-9x=7x-70

-9x-7x=-70-648

-16x=-718

x=44,875

a) x: 0,16 =9:x hay       \(\frac{x}{0,16}\)=\(\frac{9}{x}\)

\(\Rightarrow\)x.x= 0,16.9

\(\Rightarrow\)\(^{x^2}\)=1,44

\(\Rightarrow\)\(^{x^2}\)= \(^{\left(1.2\right)^2}\)

\(\Rightarrow\)x=1,2 hoặc -1,2.

b) \(\frac{72-x}{7}\)= \(\frac{x-10}{9}\)

\(\Rightarrow\)(72-x).9 = 7.(x-10)

648-9x=7x-70

-9x - 7x=-70-648

-16x=-718

\(\Rightarrow\)x= 44,875.

44,875

a) - 0,52 : x = - 9,36 : 16,38

- 0,52 : x = \(-\frac{4}{7}\)

\(x=\left(-0,52\right):\left(-\frac{4}{7}\right)=\frac{91}{100}=0,91\)

b) \(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\)

\(\frac{\frac{17}{4}}{\frac{23}{8}}=\frac{x}{1,61}\)

\(\frac{x}{1,61}=\frac{34}{23}\)

\(x=\frac{34}{23}.1,61=2,38\)

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

\(\frac{4\frac{1}{4}}{2\frac{7}{8}}=\frac{x}{1,61}\)

\(\Leftrightarrow\frac{\frac{17}{4}}{\frac{23}{8}}=\frac{x}{1,61}\)

\(\Leftrightarrow\frac{34}{23}=\frac{x}{1,61}\)

\(\Leftrightarrow x=\frac{34}{23}.1,61\)

\(\Leftrightarrow x=\frac{119}{50}\)

\(\begin{array}{l}a)\frac{x}{{ - 3}} = \frac{7}{{0,75}}\\ \Rightarrow x.0,75 = ( - 3).7\\ \Rightarrow x = \frac{{( - 3).7}}{{0,75}} =  - 28\end{array}\)

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: \(\dfrac{x}{\sqrt{5}}=\dfrac{\sqrt{5}}{x}\)

=>\(x^2=5\)

=>\(x=\pm\sqrt{5}\)