a) $$x^6 \cdot x \cdot x^3 = x^{6+1+3} = x^{10}$$
b) $$x^{18} : x^{10} : x = x^{18-10-1} = x^{7}$$
c) $$x^{25} : (x^7)^3 = x^{25} : x^{7 \cdot 3} = x^{25} : x^{21} = x^{25-21} = x^4$$
d) $$x^{12} \cdot x^6 : (x^5)^3 = x^{12+6} : x^{5 \cdot 3} = x^{18} : x^{15} = x^{18-15} = x^3$$
e) $$(x^7)^4 : (x^3)^8 = x^{7 \cdot 4} : x^{3 \cdot 8} = x^{28} : x^{24} = x^{28-24} = x^4$$
f) $$\frac{x^{21} \cdot x^5}{(x^6)^4} = \frac{x^{21+5}}{x^{6 \cdot 4}} = \frac{x^{26}}{x^{24}} = x^{26-24} = x^2$$
$$\frac{12^3 \cdot 4^7}{12^4 \cdot 4^6} = \frac{12^3}{12^4} \cdot \frac{4^7}{4^6} = \frac{1}{12} \cdot 4 = \frac{4}{12} = \frac{1}{3}$$
Ответ: $$\frac{1}{3}$$
$$5^{11} \cdot x = (5^4)^3$$
$$5^{11} \cdot x = 5^{4 \cdot 3}$$
$$5^{11} \cdot x = 5^{12}$$
$$x = \frac{5^{12}}{5^{11}}$$
$$x = 5^{12-11}$$
$$x = 5^1$$
Ответ: $$x = 5$$