\(a,\Leftrightarrow\left(2-x\right)\left(x^2+4\right)>0\Leftrightarrow2-x>0\Leftrightarrow x< 2\\ b,\Leftrightarrow x+3>0\Leftrightarrow x>-3\\ c,\Leftrightarrow\left[{}\begin{matrix}x< -3\\x>4\end{matrix}\right.\)

b: \(\Leftrightarrow x+3>0\)

hay x>-3

\(a,\dfrac{3}{4}:\dfrac{6}{x}=\dfrac{5}{4}\\ \dfrac{6}{x}=\dfrac{3}{4}:\dfrac{5}{4}\\ \dfrac{6}{x}=\dfrac{3}{5}\\ x=6:\dfrac{3}{5}\\ x=10\\ b,\left(x+\dfrac{7}{4}\right)\times\dfrac{2}{3}=6\\ x+\dfrac{7}{4}=6:\dfrac{2}{3}\\x+\dfrac{7}{4}=9\\ x=9-\dfrac{7}{4}\\ x=\dfrac{29}{4}\)

giúp mình đi, sao dạo này ít ngừi giúp qué zại

a) \(\dfrac{3}{4}\div\dfrac{6}{x}=\dfrac{5}{4}\)

            \(\dfrac{6}{x}=\dfrac{3}{4}\div\dfrac{5}{4}\)

            \(\dfrac{6}{x}=\dfrac{3}{5}\)

            \(x=\left(6\div3\right)\times5\)

           \(x=10\)

b) \(\left(x+\dfrac{7}{4}\right)\times\dfrac{2}{3}=6\)

     \(x+\dfrac{7}{4}=6\div\dfrac{2}{3}\)

     \(x+\dfrac{7}{4}=9\)

     \(x=9-\dfrac{7}{4}\)

    \(x=\dfrac{29}{4}\)

\(4\left(x-1\right)-3\left(x-2\right)=-5\)

\(\Leftrightarrow4x-4-3x+6=-5\)

\(\Leftrightarrow x=-5+4-6\)

\(\Leftrightarrow x=-7\)

Vậy x=-7

Ta có: 4(x-1) - 3(x-2) = -5

          (4x-4) - (3x-6) = -5

          4x - 4 - 3x + 6 = -5 

     (4x - 3x) + (-4+6) = -5

                       x + 2  = -5

                             x  = -5 - 2

                              x = -7

                         Vậy x = -7

tự làm là hạnh phúc của mỗi công dân.

\(-4x+2=3x-5\)

\(\Leftrightarrow-4x-3x=-5-2\)

\(\Leftrightarrow-7x=-7\)

\(\Leftrightarrow x=1\)

-4x +2=3x-5

suy ra 2+5=3x+4x

suy ra 7=7x

suy ra x=1

Vậy x=1

-4x+2=3x-5

5+2=3x+4x

7x=7

x=7:7

x=1

Nhớ k cho mik nha!!!!!

Chúc bạn học tốt!!!!!!!!!

c) \(\dfrac{x+4}{20}=\dfrac{5}{x+4}\)

⇔\(\left(x+4\right)\left(x+4\right)=100\)

⇔\(\left(x+4\right)^2=10^2\)

⇔\(\left[{}\begin{matrix}x+4=10\\x+4=-10\end{matrix}\right.\)

⇔\(\left[{}\begin{matrix}x=6\\x=-14\end{matrix}\right.\)

\(c,ĐK:x\ne-4\\ PT\Leftrightarrow\left(x+4\right)^2=100\\ \Leftrightarrow\left[{}\begin{matrix}x+4=10\\x+4=-10\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x=6\left(tm\right)\\x=-14\left(tm\right)\end{matrix}\right.\\ d,ĐK:x\ne-2;x\ne-3\\ PT\Leftrightarrow\left(x-1\right)\left(x+3\right)=\left(x-2\right)\left(x+2\right)\\ \Leftrightarrow x^2+2x-3=x^2-4\\ \Leftrightarrow2x=-1\Leftrightarrow x=-\dfrac{1}{2}\left(tm\right)\)