Giải thích các bước giải:
Ta có:
\(\begin{array}{l}
a,\\
3{x^2} + 12x - 66 = 0\\
\Leftrightarrow {x^2} + 4x - 22 = 0\\
\Leftrightarrow {x^2} + 4x + 4 = 26\\
\Leftrightarrow {\left( {x + 2} \right)^2} = 26\\
\Leftrightarrow x = - 2 \pm \sqrt {26} \\
c,\\
{x^2} + 3x - 10 = 0\\
\Leftrightarrow \left( {{x^2} - 2x} \right) + \left( {5x - 10} \right) = 0\\
\Leftrightarrow x\left( {x - 2} \right) + 5\left( {x - 2} \right) = 0\\
\Leftrightarrow \left( {x - 2} \right)\left( {x + 5} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = 2\\
x = - 5
\end{array} \right.\\
e,\\
3{x^2} - 7x + 8 = 0\\
Δ= {7^2} - 4.3.8 = - 47 < 0\\
\Rightarrow ptvn\\
g,\\
3{x^2} + 7x + 2 = 0\\
\Leftrightarrow \left( {3{x^2} + 6x} \right) + \left( {x + 2} \right) = 0\\
\Leftrightarrow 3x.\left( {x + 2} \right) + \left( {x + 2} \right) = 0\\
\Leftrightarrow \left( {x + 2} \right)\left( {3x + 1} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = - 2\\
x = - \frac{1}{3}
\end{array} \right.\\
i,\\
2{x^2} - 6x + 1 = 0\\
\Leftrightarrow 2\left( {{x^2} - 3x + \frac{9}{4}} \right) = \frac{7}{2}\\
\Leftrightarrow 2{\left( {x - \frac{3}{2}} \right)^2} = \frac{7}{2}\\
\Leftrightarrow {\left( {x - \frac{3}{2}} \right)^2} = \frac{7}{4}\\
\Leftrightarrow x = \frac{{3 \pm \sqrt 7 }}{2}
\end{array}\)
