\[\boxed{\mathbf{6.64}}\]
\[\textbf{а)}\ x > x^{2}\]
\[нет\ таких\ \text{x.}\]
\[\textbf{б)}\ x^{2} > x^{3}\]
\[x < 0.\]
\[\textbf{в)}\ x < x^{2}\]
\[x - любое\ число,\ кроме\ x = 0;\ \ \]
\[x = 1.\]
\[\textbf{г)}\ x^{2} < x^{3}\]
\[x > 1.\]
\[\textbf{д)}\ x^{2} = x^{3}\]
\[x = 0;\ \ x = 1.\]