Question

Tìm x, biết:

1. \(\left(\dfrac{2x}{5}+2\right):\left(-4\right)=-1\dfrac{1}{2}\)

2. x. ( x + 1) = 0

3. 2x - 16 = 40 + x

4. x : \(\dfrac{5}{3}\) + \(\dfrac{1}{3}\) = \(\dfrac{-2}{5}\)

5. 3\(\dfrac{1}{2}\) - \(\dfrac{1}{2}\) x = \(\dfrac{2}{3}\)

6. \(\dfrac{x}{4}=\dfrac{9}{x}\)

7. \(\dfrac{1}{3}+\dfrac{1}{2}:x=\) -0,25

Answer 1

6. \(\dfrac{x}{4}=\dfrac{9}{x}\)

=>x²=4.9=36

=>x\(\in\)\(\left\{-6;6\right\}\)

Answer 2

\((\dfrac{2x}{5}+2):\left(-4\right)=-1\dfrac{1}{2}\) 

(\(\dfrac{2x}{5}+2):\left(-4\right)=-\dfrac{3}{2}\) 

\(\dfrac{2x}{5}=-\dfrac{3}{2}.\left(-4\right)\) 

\(\dfrac{2x}{5}=6\) 

\(\dfrac{2x}{5}=\dfrac{30}{5}\) 

2x = 30 

x = 30 : 2 = 15

Answer 3

x.(x+1) = 0

⇒ \(\left\{{}\begin{matrix}x=0\\x+1=0\end{matrix}\right.\)

⇒\(\left\{{}\begin{matrix}x=0\\x=0-1\end{matrix}\right.\) 

\(\left\{{}\begin{matrix}x=0\\x=-1\end{matrix}\right.\)

3)\(2x-16=40+x\) 

  \(2x-x=40+16\)

       \(x=56\) 

Answer 4

4)x : \(\dfrac{5}{3}+\dfrac{1}{3}=-\dfrac{2}{3}\) 

  x : \(\dfrac{5}{3}=-\dfrac{2}{3}-\dfrac{1}{3}\) 

  x : \(\dfrac{5}{3}=-1\) 

  x :     \(=-1\times\dfrac{5}{3}\) 

  x :     \(=-\dfrac{5}{3}\) 

5)3\(\dfrac{1}{2}-\dfrac{1}{2}x=\dfrac{2}{3}\) 

  \(\dfrac{7}{2}-\dfrac{1}{2}x=\dfrac{2}{3}\) 

          \(\dfrac{1}{2}x=\dfrac{7}{2}-\dfrac{2}{3}\)

           \(\dfrac{1}{2}x=\dfrac{17}{6}\)

            \(x=\dfrac{17}{6}:\dfrac{1}{2}\)

            \(x=\dfrac{17}{3}\)

Answer 5

\(\dfrac{1}{3}+\dfrac{1}{2}:x=-0,25\) 

      \(\dfrac{1}{2}:x=-\dfrac{1}{4}-\dfrac{1}{3}\) 

    \(\dfrac{1}{2}:x=\dfrac{-7}{12}\) 

          \(x=\dfrac{1}{2}:-\dfrac{7}{12}\) 

          \(x=-\dfrac{6}{7}\)