\[\begin{array}{l}
\left( {x + 3} \right)\left( {{x^2} - 3x + 9} \right) - x\left( {x + 2} \right)\left( {x - 2} \right) = 15\\
\Leftrightarrow {x^3} + 27 - x\left( {{x^2} - 4} \right) = 15\\
\Leftrightarrow {x^3} + 27 - {x^3} + 4x = 15\\
\Leftrightarrow 4x = - 12\\
\Leftrightarrow x = - 3.\\
4{x^2} - 8x + 3 = 0\\
\Leftrightarrow 4{x^2} - 2x - 6x + 3 = 0\\
\Leftrightarrow 2x\left( {2x - 1} \right) - 3\left( {2x - 1} \right) = 0\\
\Leftrightarrow \left( {2x - 1} \right)\left( {2x - 3} \right) = 0\\
\Leftrightarrow \left[ \begin{array}{l}
x = \frac{1}{2}\\
x = \frac{3}{2}
\end{array} \right..
\end{array}\]
