Toán Lớp 8: Tìm x , biết :
a. (4x – 1) – (4x + 1) . (x – 2) = 12
b.(2x – 3) . (2x + 1) – (2x – 2)2 = 15
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Toán Lớp 8: Tìm x , biết :
a. (4x – 1) – (4x + 1) . (x – 2) = 12
b.(2x – 3) . (2x + 1) – (2x – 2)2 = 15
Comments ( 1 )
a)\,\left( {4x – 1} \right) – \left( {4x + 1} \right).\left( {x – 2} \right) = 12\\
\Leftrightarrow 4x – 1 – \left( {4{x^2} – 7x – 2} \right) – 12 = 0\\
\Leftrightarrow 4x – 1 – 4{x^2} + 7x + 2 – 12 = 0\\
\Leftrightarrow – 4{x^2} + 11x – 11 = 0\\
\Leftrightarrow 4{x^2} – 11x + 11 = 0\\
\Leftrightarrow {\left( {2x} \right)^2} – 2.2x.\frac{{11}}{4} + \frac{{{{11}^2}}}{{{4^2}}} – \frac{{{{11}^2}}}{{{4^2}}} + 11 = 0\\
\Leftrightarrow {\left( {2x – \frac{{11}}{4}} \right)^2} + \frac{{55}}{{16}} = 0
\end{array}\]
b)\left( {2x – 3} \right).\left( {2x + 1} \right) – {\left( {2x – 2} \right)^2} = 15\\
\Leftrightarrow 4{x^2} – 4x – 3 – 4{x^2} + 8x – 4 – 15 = 0\\
\Leftrightarrow 4x – 22 = 0\\
\Leftrightarrow x = \frac{{11}}{2}
\end{array}\]