Làm bài 3 .

Bài 3

`a)`

`(2x-1)(x-1)=0`

`<=>` \(\left[ \begin{array}{l}2x-1=0\\x-1=0\end{array} \right.\) `<=>`\(\left[ \begin{array}{l}x=\dfrac{1}{2}\\x=1\end{array} \right.\) 

Vậy `x=1/2` hoặc `x=1`

`b)`

`(2x-1)^2-(2x+1)^2=0`

`<=>` `[2x-1+(2x+1)].[2x-1-(2x+1)]=0`

`<=>` `(2x-1+2x+1)(2x-1-2x-1)=0`

`<=>` `4x.(-2)=0`

`<=>` `-8x=0`

`<=>` `x=0`

Vậy `x=0`

`c)`

`x^2-5x+4=0`

`<=>` `(x^2-x)+(-4x+4)=0`

`<=>` `x(x-1)-4(x-1)=0`

`<=>` `(x-1)(x-4)=0`

`<=>` \(\left[ \begin{array}{l}x-1=0\\x-4=0\end{array} \right.\)`<=>` \(\left[ \begin{array}{l}x=1\\x=4\end{array} \right.\) 

Vậy `x=1` hoặc `x=4`