Question

Tìm x thuộc Z biết :

( x - 3 ).( 5 - x ) ≥ 0

Answer 1

(x - 3) . (5 - x) \(\ge\) 0

\(\Rightarrow\) \(\left\{\begin{matrix}x-3\ge0\\5-x\ge0\end{matrix}\right.\)

\(\Rightarrow\) x \(\in\) {0; 1; 2; 3; 4; 5}

Vậy ...

Answer 2

( x-3 ) ( x-5 ) < 0

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

\(\Rightarrow\) 5 < x < 3

\(\Rightarrow\) x \(\in\) {\(\varnothing\)}

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

\(\Rightarrow\)3 < x < 5

\(\Rightarrow\) x = 4