Toán Lớp 8: Tìm x
a, 2x^2+3x-5=0
b, (x-2)(x^2+4)=x-2
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Toán Lớp 8: Tìm x
a, 2x^2+3x-5=0
b, (x-2)(x^2+4)=x-2
Comments ( 1 )
a)2{x^2} + 3x – 5 = 0\\
\Leftrightarrow 2{x^2} – 2x + 5x – 5 = 0\\
\Leftrightarrow 2x\left( {x – 1} \right) + 5\left( {x – 1} \right) = 0\\
\Leftrightarrow \left( {2x + 5} \right)\left( {x – 1} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x – 1 = 0\\
2x + 5 = 0
\end{array} \right.\,\, \Leftrightarrow \left[ \begin{array}{l}
x = 1\\
x = \frac{{ – 5}}{2}
\end{array} \right.\\
b)(x – 2)({x^2} + 4) = x – 2\\
\Leftrightarrow (x – 2)({x^2} + 4) – (x – 2) = 0\\
\Leftrightarrow (x – 2)({x^2} + 3) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x – 2 = 0\\
{x^2} + 3 = 0
\end{array} \right.\,\, \Leftrightarrow \left[ \begin{array}{l}
x = 2\\
{x^2} + 3 = 0(vo\,\,li)
\end{array} \right.\,\,\,\,\\
\end{array}\]