4) (a)840-264 80+90=と りこう

4) $$(a^n)^8 \cdot a^{40} = a^{64}$$ $$a^{8n} \cdot a^{40} = a^{64}$$ $$a^{8n+40} = a^{64}$$ $$8n+40 = 64$$ $$8n = 64 - 40$$ $$8n = 24$$ $$n = \frac{24}{8}$$ $$n=3$$

Ответ: $$n = 3$$