$\displaystyle \begin{array}{{>{\displaystyle}l}} ( x-1)^{2} =x-1\ \\ chia\ hai\ vế\ cho\ x-1\ ta\ có\ \\ x-1=1\ \\ \rightarrow x=2\ \\ Vậy....\ \\ b) \ ( 2x-1)^{2} -25=0\ \\ \rightarrow ( 2x-1+5)( 2x-1-5) =0\ \\ ( 2x+4)( 2x-6) =0\ \\ \left[ \begin{array}{l l} 2x+4=0 & \\ 2x-6=0 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=-2 & \\ x=3 & \end{array} \right. \ \\ c) 8x^{3} -50x=0\\ \rightarrow 2x\left( 4x^{2} -25\right) =0\\ \rightarrow 2x( 2x-5)( 2x+5) =0\ \\ \rightarrow \left[ \begin{array}{l l} x=0 & \\ 2x-5=0 & \\ 2x+5=0 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=0 & \\ x=\frac{5}{2} & \\ x=\frac{-5}{2} & \end{array} \right. \ \\ d) 3x( x-1) +x-1=0\ \\ ( x-1)( 3x+1) =0\ \\ \rightarrow \left[ \begin{array}{l l} x-1=0 & \\ 3x+1=0 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=1 & \\ x=\frac{-1}{3} & \ \end{array} \right.\\ e) 2( x+3) -x^{2} -3x=0\ \\ 2( x+3) -x( x+3) =0\ \\ ( x+3)( 2-x) =0\ \\ \left[ \begin{array}{l l} x+3=0 & \\ 2-x=0 & \end{array} \right.\rightarrow \left[ \begin{array}{l l} x=-3 & \\ x=2 & \end{array} \right. \ \\ f) 4x^{2} -25-( 2x-5)( 2x+7) =0\ \\ ( 2x-5)( 2x+5) -( 2x-5)( 2x+7) =0\ \\ ( 2x-5)( 2x+5-2x-7) =0\ \\ -2( 2x-5) =0\ \\ \rightarrow 2x-5=0\ \\ \rightarrow x=\frac{5}{2} \ \end{array}$
