`7x(2x-3)=8x - 12`

Đáp án:

`7x(2x−3)=8x−12`

`14x^2-21x=8x-12`

`14x^2−21x−( 8x−1 2 )=0`

`14x^2−21x− 8x+1 2 =0`

`14x^2−8x− 21x+12 =0`

`(14x^2-8x)+(-21x+12)=0`

`2x ( 7x− 4 ) − 3 ( 7x − 4 ) = 0`

`(2x-3)(7x-4)=0`

`⇔` \(\left[ \begin{array}{l}2x-3=0\\7x-4=0\end{array} \right.\) 

`⇔` \(\left[ \begin{array}{l}2x=0+3\\7x=0+4\end{array} \right.\) 

`⇔` \(\left[ \begin{array}{l}2x=3\\7x=4\end{array} \right.\) 

`⇔` \(\left[ \begin{array}{l}x=3:2\\x=4:7\end{array} \right.\) 

`⇔` \(\left[ \begin{array}{l}x=\frac{3}{2}\\x=\frac{4}{7}\end{array} \right.\) 

`⇒S={3/2 ; 4/7 }`