Toán Lớp 8: Tìm x : 4x(x-5) – (2x-1)(1+2x)=5
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Toán Lớp 8: Tìm x : 4x(x-5) – (2x-1)(1+2x)=5
Comments ( 2 )
4x\left( {x – 5} \right)–\left( {2x – 1} \right)\left( {1 + 2x} \right) = 5\\
\Leftrightarrow 4{x^2} – 20x – \left( {2x – 1} \right)\left( {2x + 1} \right) = 5\\
\Leftrightarrow 4{x^2} – 20x – \left[ {2x\left( {2x + 1} \right) – \left( {2x + 1} \right)} \right] = 5\\
\Leftrightarrow 4{x^2} – 20x – \left( {4{x^2} + 2x – 2x – 1} \right) = 5\\
\Leftrightarrow 4{x^2} – 20x – \left( {4{x^2} – 1} \right) = 5\\
\Leftrightarrow \;4{x^2} – 20x – 4{x^2} + 1 = 5\\
\Leftrightarrow – 20x + 1 = 5\\
\Leftrightarrow – 20x = 4\\
\Leftrightarrow x = – \frac{1}{5}
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