Toán Lớp 8: b) (2x + 1)2 – 2x – 12 = ( x + 1)2
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Toán Lớp 8: b) (2x + 1)2 – 2x – 12 = ( x + 1)2
Comments ( 2 )
{\left( {2x{\rm{ }} + {\rm{ }}1} \right)^2}{\rm{ }} – {\rm{ }}2x{\rm{ }} – {\rm{ }}12{\rm{ }} = {\rm{ }}{\left( {{\rm{ }}x{\rm{ }} + {\rm{ }}1} \right)^2}\\
(4{x^2} + 4x + 1) – 2x – 12 = ({x^2} + x + 1)\\
4{x^2} + 4x + 1 – 2x – 12 = {x^2} + x + 1\\
4{x^2} + 2x – 11 – {x^2} – 2x – 1 = 0\\
3{x^2} – 12 = 0\\
3({x^2} – 4) = 0\\
3(x – 2)(x + 2) = 0\\
= > \begin{array}{*{20}{c}}
{x – 2 = 0 \to x = 2}\\
{x + 2 = 0 \to x = – 2}
\end{array}
\end{array}\]