Toán Lớp 7: tìm x .a.(2x-1)^3=-8 b. lx-1,5l+l2,5-xl=0 trả lời giúp em với ạ
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Toán Lớp 7: tìm x .a.(2x-1)^3=-8 b. lx-1,5l+l2,5-xl=0 trả lời giúp em với ạ
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a){\left( {2x – 1} \right)^3} = – 8\\
\Leftrightarrow {\left( {2x – 1} \right)^3} = {\left( { – 2} \right)^3}\\
\Leftrightarrow 2x – 1 = – 2\\
\Leftrightarrow 2x = – 1\\
\Leftrightarrow x = – \dfrac{1}{2}\\
Vậy\,x = – \dfrac{1}{2}\\
b)\left| {x – 1,5} \right| + \left| {2,5 – x} \right| = 0\\
Do:\left\{ \begin{array}{l}
\left| {x – 1,5} \right| \ge 0\\
\left| {2,5 – x} \right| \ge 0
\end{array} \right.\\
\Leftrightarrow \left| {x – 1,5} \right| + \left| {2,5 – x} \right| \ge 0\\
Khi:\left| {x – 1,5} \right| + \left| {2,5 – x} \right| = 0\\
\Leftrightarrow \left\{ \begin{array}{l}
\left| {x – 1,5} \right| = 0\\
\left| {2,5 – x} \right| = 0
\end{array} \right.\\
\Leftrightarrow \left\{ \begin{array}{l}
x = 1,5\\
x = 2,5
\end{array} \right.\left( {ktm} \right)
\end{array}$