Đáp án:
a) \(\left[ \begin{array}{l}
x = 0\\
x = - 8
\end{array} \right.\)
b) \(x \in \emptyset \)
c) \(\left[ \begin{array}{l}
x = 0\\
x = 5\\
x = 10\\
x = 15\\
....
\end{array} \right.\)
Giải thích các bước giải:
\(\begin{array}{l}
a) - x.\left( {8 + x} \right) = 0\\
\to \left[ \begin{array}{l}
x = 0\\
x = - 8
\end{array} \right.\\
b)\left| x \right| - \left| { - x + 3} \right| = 7\\
\to x - \left( {x - 3} \right) = 7\left( {do:0 < x < 3} \right)\\
\to x - x + 3 = 7\\
\to 3 = 7\left( {KTM} \right)\\
\to x \in \emptyset \\
c)x + 5 \vdots 5\\
\to x + 5 \in B\left( 5 \right)\\
\to \left[ \begin{array}{l}
x + 5 = 5\\
x + 5 = 10\\
x + 5 = 15\\
x + 5 = 20\\
....
\end{array} \right. \to \left[ \begin{array}{l}
x = 0\\
x = 5\\
x = 10\\
x = 15\\
....
\end{array} \right.
\end{array}\)
