\[1)\ z = 6x^{2}i + 2xi - 5x^{2}\]
\[z = - 5x^{2} + \left( 6x^{2} + 2x \right)i\]
\[6x^{2} + 2x = 0\]
\[2x(3x + 1) = 0\]
\[x_{1} = - \frac{1}{3};\ \ \ x_{2} = 0.\]
\[Ответ:\ - \frac{1}{3};\ 0.\]
\[2)\ z = (x - 3xi) + \left( 5 + x^{2}i \right)\]
\[z = (x + 5) + \left( x^{2} - 3x \right)i\]
\[x^{2} - 3x = 0\]
\[x(x - 3) = 0\]
\[x_{1} = 0;\ \ x_{2} = 3.\]
\[Ответ:\ \ 0;\ 3.\]