Toán Lớp 6: a) (x + 2)2 = 4 c) 5 . (2x + 1)2 = 245
b) (4x – 1)3 = 27 d) 720 : [45 – (5 – 2x)3] = 23 . 5
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Toán Lớp 6: a) (x + 2)2 = 4 c) 5 . (2x + 1)2 = 245
b) (4x – 1)3 = 27 d) 720 : [45 – (5 – 2x)3] = 23 . 5
Comments ( 1 )
a)\left[ \begin{array}{l}
x = 0\\
x = – 4
\end{array} \right.\\
b)x = 1\\
c)\left[ \begin{array}{l}
x = 3\\
x = – 4
\end{array} \right.
\end{array}\)
a){\left( {x + 2} \right)^2} = 4\\
\to \left| {x + 2} \right| = 2\\
\to \left[ \begin{array}{l}
x + 2 = 2\\
x + 2 = – 2
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 0\\
x = – 4
\end{array} \right.\\
b){\left( {4x – 1} \right)^3} = 27\\
\to \sqrt[3]{{{{\left( {4x – 1} \right)}^3}}} = \sqrt[3]{{{3^3}}}\\
\to 4x – 1 = 3\\
\to 4x = 4\\
\to x = 1\\
c)5{\left( {2x + 1} \right)^2} = 245\\
\to {\left( {2x + 1} \right)^2} = 49\\
\to \left| {2x + 1} \right| = 7\\
\to \left[ \begin{array}{l}
2x + 1 = 7\\
2x + 1 = – 7
\end{array} \right.\\
\to \left[ \begin{array}{l}
x = 3\\
x = – 4
\end{array} \right.\\
\end{array}\)
d)720:\left[ {45 – {{\left( {5 – 2x} \right)}^3}} \right] = {2^3}.5\\
\to 45 – {\left( {5 – 2x} \right)^3} = 720:\left( {8.5} \right)\\
\to 45 – {\left( {5 – 2x} \right)^3} = 720:40\\
\to 45 – {\left( {5 – 2x} \right)^3} = 18\\
\to {\left( {5 – 2x} \right)^3} = 27\\
\to 5 – 2x = 3\\
\to 2x = 2\\
\to x = 1
\end{array}\)