\(\left(x+\frac{2}{3}\right)\left(\frac{5}{4}-2x\right)>0\)

th1 : 

\(\hept{\begin{cases}x+\frac{2}{3}>0\\\frac{5}{4}-2x>0\end{cases}\Rightarrow\hept{\begin{cases}x>-\frac{2}{3}\\-2x>-\frac{5}{4}\end{cases}\Rightarrow}\hept{\begin{cases}x>-\frac{2}{3}\\x>\frac{5}{8}\end{cases}\Rightarrow}x>\frac{5}{8}}\)

th2 : 

\(\hept{\begin{cases}x+\frac{2}{3}< 0\\\frac{5}{4}-2x< 0\end{cases}\Rightarrow\hept{\begin{cases}x< -\frac{2}{3}\\-2x< -\frac{5}{4}\end{cases}\Rightarrow}\hept{\begin{cases}x< -\frac{2}{3}\\x< \frac{5}{8}\end{cases}\Rightarrow}x< -\frac{2}{3}}\)

vậy_

x=20

\(70:\dfrac{4x+720}{x}=\dfrac{1}{2}\)

\(\Rightarrow\dfrac{4x+720}{x}=70:\dfrac{1}{2}=140\)

\(\Rightarrow4x+720=140.x\)

\(\Rightarrow720=36.x\)

\(\Rightarrow720:36=x\)

\(\Rightarrow x=20\)

Đk : x khác 0 

=> 35/2x + 720/x = 1/2

=> 35+1440/2x = 1/2

=> 1475/2x = 1/2

=> 1475 = 1/2 . 2x = x

Vậy x = 1475

k mk nha

X=1475

90/17

1111111111111111111111111111111111111111111111111111111111111111111111111111111

\(\frac{4x+720}{70\times x}=\frac{1}{2}\Rightarrow2\left(4x+720\right)=70x\)

<=>8x+1440=70x

 =>8x-70x=0-1440

=>-62x=-1440

=>x=\(\frac{720}{31}\)

70:4x + 720/x = 1/2

=> 70/4x + 2880/4x = 1/2

=> 2950/4x = 1/2

=> x = 1475

\(\Leftrightarrow8x+1440=x\)

=>7x=-1440

hay x=-1440/7

Giải:

a) \(70.\dfrac{4x+720}{x}=\dfrac{1}{2}\)

\(\Leftrightarrow\dfrac{280x+50400}{x}=\dfrac{1}{2}\)

\(\Leftrightarrow2\left(280x+50400\right)=x\)

\(\Leftrightarrow560x+100800=x\)

\(\Leftrightarrow560x-x=-100800\)

\(\Leftrightarrow549x=-100800\)

\(\Leftrightarrow x=-\dfrac{11200}{61}\)

Vậy ...

b) \(x^2+5x< 0\)

\(\Leftrightarrow x\left(x+5\right)< 0\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x< 0\\x+5>0\end{matrix}\right.\\\left\{{}\begin{matrix}x>0\\x+5< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x< 0\\x>-5\end{matrix}\right.\\\left\{{}\begin{matrix}x>0\\x< -5\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}0>x>-5\\x\in\varnothing\end{matrix}\right.\)

Vậy ...

Ta co:4x+720/x=70/1/2

4x+720/x=140

Gặp cả 2 vế lên x lan,ta co

4x+720=140x

720=136x(bớt cả 2 vế đi 4x)

x=720/136=