Môn Toán Lớp 8: a) | x + 2 | = 3x – 5 c) |2x | = x – 6
b) |-3x | = x – 8 d) | 6 – 2x | = x + 4
giải bằng 2 trg hợp ạ
Môn Toán Lớp 8: a) | x + 2 | = 3x – 5 c) |2x | = x – 6 b) |-3x | = x – 8 d) | 6 – 2x | = x +
a)Dkxd:3x – 5 \ge 0\\
\Leftrightarrow 3x \ge 5\\
\Leftrightarrow x \ge \dfrac{5}{3}\\
\left| {x + 2} \right| = 3x – 5\\
\Leftrightarrow x + 2 = 3x – 5\\
\Leftrightarrow 3x – x = 2 + 5\\
\Leftrightarrow 2x = 7\\
\Leftrightarrow x = \dfrac{7}{2}\left( {tm} \right)\\
Vậy\,x = \dfrac{7}{2}\\
b)Dkxd:x \ge 8\\
\left| { – 3x} \right| = x – 8\\
\Leftrightarrow \left| {3x} \right| = x – 8\\
\Leftrightarrow 3x = x – 8\\
\Leftrightarrow 3x – x = – 8\\
\Leftrightarrow 2x = – 8\\
\Leftrightarrow x = – 4\left( {ktm} \right)\\
Vậy\,x \in \emptyset \\
c)Dkxd:x \ge 6\\
\left| {2x} \right| = x – 6\\
\Leftrightarrow 2x = x – 6\\
\Leftrightarrow 2x – x = – 6\\
\Leftrightarrow x = – 6\left( {ktm} \right)\\
Vậy\,x \in \emptyset \\
d)Dkxd:x \ge – 4\\
\left| {6 – 2x} \right| = x + 4\\
\Leftrightarrow \left| {2x – 6} \right| = x + 4\\
\Leftrightarrow \left[ \begin{array}{l}
2x – 6 = x + 4\\
2x – 6 = – x – 4
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
2x – x = 4 + 6\\
2x + x = – 4 + 6
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 10\left( {tm} \right)\\
3x = 2
\end{array} \right.\\
\Leftrightarrow \left[ \begin{array}{l}
x = 10\\
x = \dfrac{2}{3}\left( {tm} \right)
\end{array} \right.\\
Vậy\,x = 10;x = \dfrac{2}{3}
\end{array}$