Используем свойства степеней:
\[ x^8 \cdot x^2 = x^{8+2} = x^{10} \]
\[ x^8 : x^2 = x^{8-2} = x^{6} \]
\[ (x^8)^2 = x^{8 \cdot 2} = x^{16} \]
\[ \frac{(x^4)^5 \cdot x^2}{x^{12}} = \frac{x^{4 \cdot 5} \cdot x^2}{x^{12}} = \frac{x^{20} \cdot x^2}{x^{12}} = \frac{x^{20+2}}{x^{12}} = \frac{x^{22}}{x^{12}} = x^{22-12} = x^{10} \]
Ответ: 1) \( x^{10} \); 2) \( x^6 \); 3) \( x^{16} \); 4) \( x^{10} \).