Question

Tìm x biết: (x+5)(x-1)>0

Answer 1

(x + 5)(x - 1) > 0

=> x + 5 và x + 1 cùng dấu

=> \(\left[{}\begin{matrix}\left\{{}\begin{matrix}x+5< 0\\x-1< 0\end{matrix}\right.\\\left\{{}\begin{matrix}x+5>0\\x-1>0\end{matrix}\right.\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}\left\{{}\begin{matrix}x< -5\\x< 1\end{matrix}\right.\\\left\{{}\begin{matrix}x>-5\\x>1\end{matrix}\right.\end{matrix}\right.\)

=> \(\left[{}\begin{matrix}x< -5\\x>1\end{matrix}\right.\)

Vậy x < -5 hoặc x > 1 t/m

Answer 2

\(\left(x+5\right)\left(x-1\right)>0.\)

\(\Rightarrow x+5\) và \(x-1\) cùng dấu.

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x+5>0\\x-1>0\end{matrix}\right.\\\left\{{}\begin{matrix}x+5< 0\\x-1< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>-5\\x>1\end{matrix}\right.\\\left\{{}\begin{matrix}x< -5\\x< 1\end{matrix}\right.\end{matrix}\right.\)\(\Leftrightarrow\left[{}\begin{matrix}x>1\\x< -5\end{matrix}\right..\)

Vậy..........