Question

tìm x biết

a) 2x (x - 7) + 5x - 35 = 0

b) x (x - 3) - 7x + 21 = 0

 

Answer 1

  

Answer 2

`a)` `2x (x -` `7) + 5x` `- 35 = 0`

`=>` `2x (x` `- 7) +` `5(x -` `7) = 0`

`=> (``2x + 5``) (x -` `7) = 0`

`=>` $\left[\begin{matrix} 2x + 5 = 0\\ x - 7 = 0\end{matrix}\right.$

`=>` $\left[\begin{matrix} 2x = -5\\ x = 7\end{matrix}\right.$

`=>` $\left[\begin{matrix} x = \dfrac{-5}{2}\\ x = 7\end{matrix}\right.$

`b)` `x (x -` `3) - 7x` `+ 21 = 0`

`=>` `x(x` `- 3) -` `7(x -` `3) = 0`

`=> (``x - 7``) (x -` `3) = 0`

`=>` $\left[\begin{matrix} x - 7 = 0\\ x - 3 = 0\end{matrix}\right.$

`=>` $\left[\begin{matrix} x = 7\\ x = 3\end{matrix}\right.$