Đáp án:
`g) 2(x-2)-x^2+4x-4=0`
`<=> 2(x-2)-(x^2-4x+4)=0`
`<=> 2(x-2)-(x-2)^2=0`
`<=> (x-2)(2-x+2)=0`
`<=> (x-2)(4-x)=0`
`<=>`\(\left[ \begin{array}{l}x-2=0\\4-x=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=2\\x=4\end{array} \right.\)
`h) x(x-5)-4x+20=0`
`<=> x(x-5)-4(x-5)=0`
`<=> (x-5)(x-4)=0`
`<=>` \(\left[ \begin{array}{l}x-5=0\\x-4=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=5\\x=4\end{array} \right.\)
`i) x(x+6)-7x-42=0`
`<=> x(x+6)-7(x+6)=0`
`<=> (x+6)(x-7)=0`
`<=>`\(\left[ \begin{array}{l}x+6=0\\x-7=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=-6\\x=7\end{array} \right.\)
`k) x^3-5x^2+x-5=0`
`<=>x^2(x-5)+(x-5)=0`
`<=>(x-5)(x^2+1)=0`
do `x^2>=0<=>x^2+1>=1>0` với mọi `x`
`=>x-5=0<=>x=5`
`l) x^4-2x^3+10x-20=0`
`<=>x^3(x-2)+10(x-2)=0`
`<=>(x^3+10)(x-2)=0`
`<=>`\(\left[ \begin{array}{l}x^3+10=0\\x-2=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x^3=10\\x=2\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=∛10\\x=2\end{array} \right.\)
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