Toán Lớp 8: Tìm x:
(x + 3)2 – (x – 4)(x + 8) = 1
3(x + 2)2 + (2x – 1)2 – 7(x + 3)(x – 3) = 36
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Toán Lớp 8: Tìm x:
(x + 3)2 – (x – 4)(x + 8) = 1
3(x + 2)2 + (2x – 1)2 – 7(x + 3)(x – 3) = 36
Comments ( 2 )
{\left( {x + 3} \right)^2} – \left( {x – 4} \right)\left( {x + 8} \right) = 1\\
\Leftrightarrow {x^2} + 6x + 9 – {x^2} + 8x – 4x – 32 = 1\\
\Leftrightarrow {x^2} + 6x + 9 – ({x^2} + 4x – 32) = 1\\
\Leftrightarrow {x^2} + 6x + 9 – {x^2} – 4x + 32 = 1\\
\Leftrightarrow 2x + 41 = 1\\
\Leftrightarrow 2x = – 40\\
\Leftrightarrow x = – 20\\
3{\left( {x + 2} \right)^2} + {\left( {2x – 1} \right)^2} – 7\left( {x + 3} \right)\left( {x – 3} \right) = 36\\
\Leftrightarrow 3({x^2} + 4x + 4) + (4{x^2} – 4x + 1) – 7({x^2} – 9) = 36\\
\Leftrightarrow 3{\left( {x + 2} \right)^2} + {\left( {2x – 1} \right)^2} – 7\left( {x + 3} \right)\left( {x – 3} \right) = 36\\
\Leftrightarrow 8x + 76 = 36\\
\Leftrightarrow 8x = – 40\\
\Leftrightarrow \;x = – 5
\end{array}\]