Tìm $x^{}$, biết: a) $x(x-1)-x^{2}+2x=5$  b) $4x^{3}-36x=0$  c) $2x^{2}-2x=(x-1)^2$  d) $(x-7)(x^{2}-9x+20)(x-2)=72$

` a)x(x-1)-x^2+2x=5 `

` =>x^2-x-x^2+2x=5 `

` =>x=5 `

` b)4x^3-36x=0 `

` =>4x(x^2-9)=0 `

` => ` \(\left[ \begin{array}{l}4x=0\\x^2-9=0\end{array} \right.\) ` => ` \(\left[ \begin{array}{l}x=0\\x^2=9\end{array} \right.\) ` => ` \(\left[ \begin{array}{l}x=0\\x=±3\end{array} \right.\)

` c)2x^2-2x=(x-1)^2 `

` =>2x^2-2x=x^2-2x+1 `

` =>2x^2-2x-x^2+2x=1 `

` =>x^2=1 =>x=±1 `

` d)(x-7)(x^2-9x+20)(x-2)=72 `

` =>(x-7)(x^2-9x+20)(x-2)-72=0 `

` =>(x^3-9x^2+20x-7x^2+63x-140)(x-2)-72=0 `

` =>(x^3-16x^2+83x-140)(x-2)-72=0 `

` =>x^4-16x^3+83x^2-140x-2x^3+32x^2-166x+280-72=0 `

` =>x^4-18x^3+115x^2-306x+208=0 `

` =>x^4-10x^3+35x^2-26x-8x^3+80x^2-280x+208=0 `

` =>x(x^3-10x^2+35x-26)-8(x^3-10x^2+35x-26)=0 `

` =>(x-8)(x^3-10x^2+35x-26)=0 `

` =>(x-8)(x^3-9x^2+26x-x^2+9x-26)=0 `

` =>(x-8)[x(x^2-9x+26)-(x^2+9x-26)]=0 `

` =>(x-8)(x-1)(x^2-9x+26)=0 `

` => ` \(\left[ \begin{array}{l}x-8=0\\x-1=0\\x^2-9x+26=0\end{array} \right.\) 

` => ` \(\left[ \begin{array}{l}x=8\\x=1\\x^2-2.x.\dfrac{9}{2}+(\dfrac{9}{2})^2+\dfrac{23}{4}=0\end{array} \right.\) 

` => ` \(\left[ \begin{array}{l}x=8\\x=1\\(x-\dfrac{9}{2})^2=-\dfrac{23}{4}\end{array} \right.\) 

` => ` \(\left[ \begin{array}{l}x=8\\x=1\\x∈∅.(x-\dfrac{9}{2})^2≥0∀x\end{array} \right.\)