Đáp án:
`1, x^2+5x=0`
`⇔x(x+5)=0`
`⇔`\(\left[ \begin{array}{l}x=0\\x+5=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=0\\x=-5\end{array} \right.\)
`2, (x/2-3)(x+1/3)=0`
`⇔x/2-3=0` hoặc `x+1/3=0`
`⇔x/2=3` hoặc `x=-1/3`
`⇔x=6` hoặc `x=-1/3`
`3, (2x-1)(x+3)(2-x)=0`
`⇔2x-1=0` hoặc `x+3=0` hoặc `2-x=0`
`⇔2x=1` hoặc `x=-3` hoặc `x=2`
`⇔x=1/2` hoặc `x=-3` hoặc `x=2`
`4, x(x-2)-5x+10=0`
`⇔x(x-2)-5(x-2)=0`
`⇔(x-2)(x-5)=0`
`⇔`\(\left[ \begin{array}{l}x-2=0\\x-5=0\end{array} \right.\)
`<=>`\(\left[ \begin{array}{l}x=2\\x=5\end{array} \right.\)
`5, x^3-5x^2+4x-20=0`
`⇔x^2(x-5)+4(x-5)=0`
`⇔(x-5)(x^2+4)=0` (1)
do `x^2>=0⇔x^2+4>=4>0`
`(1)=> x-5=0<=>x=5`
