Question

tìm x biết: a) (x-1)(x-3)<0

b)3x+x\(^2\)=0

Answer 1

a) \((x-1)(x-3)<0\)

\(\Rightarrow\left\{{}\begin{matrix}x-1< 0\\x-3>0\end{matrix}\right.\) hoặc \(\left\{{}\begin{matrix}x-1>0\\x-3< 0\end{matrix}\right.\)

\(\Rightarrow\left\{{}\begin{matrix}x< 1\\x>3\end{matrix}\right.\left(loại\right)\) hoặc \(\left\{{}\begin{matrix}x>1\\x< 3\end{matrix}\right.\)

\(\Rightarrow1< x< 3\)

Vậy \(1< x< 3\)

b) \(3x+x^2=0\)

\(\Rightarrow x\left(x+3\right)=0\)

\(\Rightarrow\left[{}\begin{matrix}x=0\\x+3=0\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x=0\\x=-3\end{matrix}\right.\)

Vậy \(x\in\left\{0;-3\right\}\)