Question

( x - 5 ) . ( x + 3 ) > 0

Answer 1

Theo bài ra ta có: (x-5).(x+3)>0

\(\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-5>0\\x+3>0\end{matrix}\right.\\\left\{{}\begin{matrix}x-5< 0\\x+3< 0\end{matrix}\right.\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>5\\x>-3\end{matrix}\right.\\\left\{{}\begin{matrix}x< 5\\x< -3\end{matrix}\right.\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}5< x>-3\\5>x< -3\end{matrix}\right.\Rightarrow\left[{}\begin{matrix}x>5\\x< -3\end{matrix}\right.\)

Vậy x\(\in\varnothing\)

Answer 2

Giải:

\(\left(x-5\right)\left(x+3\right)>0\)

\(\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x-5>0\\x+3>0\end{matrix}\right.\\\left\{{}\begin{matrix}x-5< 0\\x+3< 0\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}\left\{{}\begin{matrix}x>5\\x>-3\end{matrix}\right.\\\left\{{}\begin{matrix}x< 5\\x< -3\end{matrix}\right.\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}5< x>-3\\5>x< -3\end{matrix}\right.\Leftrightarrow\left[{}\begin{matrix}x>5\\x< -3\end{matrix}\right.\)

Vậy ...

Answer 3