Đáp án:
a) `x^2 + 5x`
`=> x(x +5) =0`
$\Rightarrow \left[\begin{matrix} x=0\\ x+5=0\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x=0\\ x=-5\end{matrix}\right.$
Vậy `S={0;-5}`
b) ` 3x^2 - 4x `
`=> x(3x - 4) =0`
$\Rightarrow \left[\begin{matrix} x=0\\ 3x -4=0\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x=0\\ 3x = 4\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x=0\\ x = \dfrac{4}{3}\end{matrix}\right.$
Vậy `S={0 ; 4/3}`
c) `5x^5 + 10x`
`=> 5x(x^4 + 2)=0`
$\Rightarrow \left[\begin{matrix} 5x=0\\ x^4+2=0\end{matrix}\right.$
$\Rightarrow \left[\begin{matrix} x=0\\ x^4 =-2\end{matrix}\right.$
Vậy : `S={0}`
d. `x^3 + 27`
`=> x^3 = -27`
`=>x = -3`
`S ={-3}`
mong ctlhn ạ~~
