Question

Tìm x 

a) 6x.(x-1999)-x+1999=0

b) x^2-9-4.(x+3)=0

Answer 1

`a)6x(x-1999)-x+1999=0`

`<=>6x(x-1999)-(x-1999)=0`

`<=>(x-1999)(6x-1)=0`

`<=>` \(\left[ \begin{array}{l}x-1999=0\\6x-1=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=1999\\x=\dfrac16\end{array} \right.\) 

`b)x^2-9-4(x+3)=0`

`<=>(x-3)(x+3)-4(x+3)=0`

`<=>(x+3)(x-3-4)=0`

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

`<=>` \(\left[ \begin{array}{l}x+3=0\\x-7=0\end{array} \right.\) 

`<=>` \(\left[ \begin{array}{l}x=7\\x=-3\end{array} \right.\) 

Answer 2

\(\Leftrightarrow\left(x+3\right)\left(x-7\right)=0\)

\(\Leftrightarrow\left[{}\begin{matrix}x=-3\\x=7\end{matrix}\right.\)

Vậy ...