17) a²n:a= 1

17) $$\frac{a^{2n} : a^7}{a^7} = 1$$ $$\frac{a^{2n-7}}{a^7} = 1$$ $$a^{2n-7-7} = 1$$ $$a^{2n-14} = 1$$ $$a^{2n-14} = a^0$$ $$2n-14 = 0$$ $$2n = 14$$ $$n = \frac{14}{2}$$ $$n = 7$$

Ответ: $$n = 7$$