Đáp án:
`a)` `-4 . x = -20`
`x = -20 : (-4)`
`x = 5`
`b)` `x . (-8) = 54`
`x = 54 : (-8)`
`x = -6,75`
`c)` `10 . x = -180`
`x = -180 : 10`
`x = -18`
`d)` `x . (-4) = -40`
`x = -40 : (-4)`
`x = 10`
`e)` `x . (2 - x)`
$⇔ \left[\begin{array}{l} x = 0\\2 - x = 0\end{array} \right.$
$⇔ \left[\begin{array}{l} x = 0\\x = 2\end{array} \right.$
`g` `5 . (3x - 21) = 0`
`3x - 21 = 0 : 5`
`3x - 21 = 0`
`3x = 0 + 21`
`3x = 21`
`x = 21 : 3`
`x = 7`
`h)` `8 . x(-5 - x) = 0`
$⇔\left[\begin{array}{l} x=0\\-5-x=0\end{array} \right.$
$⇔\left[\begin{array}{l} x=0\\x=-5\end{array} \right.$
`i)` `(8 + x) . (6 - x) = 0`
$⇔\left[\begin{array}{l} 8+x=0\\6-x=0\end{array} \right.$
$⇔\left[\begin{array}{l} x=-8\\x=6\end{array} \right.$
Xin Câu trả lời hay nhất!
