tìm x biết : a) 4x^2-9-x(2x-3)=0 ; b) 4x^2-12x + 9 =0

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

`4x^2 - 2x^2 + 3x - 9 = 0`

`2x^2 + 3x - 9 = 0`

`2x^2 - 3x + 6x - 9 =0`

`x(2x - 3) + 3(2x - 3) = 0`

`(2x-3)(x+3)=0`

⇒ \(\left[ \begin{array}{l}2x-3=0\\x+3=0\end{array} \right.\) 

⇒ \(\left[ \begin{array}{l}x=3/2\\x=-3\end{array} \right.\) 

b) `4x^2 - 12x+9=0`

`4x^2 - 6x - 6x + 9 =0`

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

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

`(2x-3)^2 = 0`

⇒ `2x-3 = 0`

`2x = 3`

`x=3/2`