Đáp án+Giải thích các bước giải:
`(x-2)(x+5)=0`
\(⇔\left[ \begin{array}{l}x-2=0\\x+5=0\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=0+2\\x=0-5\end{array} \right.\)
\(⇔\left[ \begin{array}{l}x=2\\x=-5\end{array} \right.\)
Vậy `x\in\{2;-5\}`
`(20-x)/10=x/5`
`⇔5(20-x)=10.x`
`⇔100-5x=10x`
`⇔10x+5x=100`
`⇔15x=100`
`⇔x=100/15`
`⇔x=20/3`
Vậy `x=20/3`
