1) $$a^5 \cdot a^7 \cdot a = a^{5+7+1} = a^{13}$$
2) $$-5m^4n^7 \cdot 2m^3n = -5 \cdot 2 \cdot m^{4+3} \cdot n^{7+1} = -10m^7n^8$$
3) $$(-4a^5b)^2 = (-4)^2 \cdot (a^5)^2 \cdot b^2 = 16a^{5 \cdot 2}b^2 = 16a^{10}b^2$$
Ответ: 1) $$a^{13}$$, 2) $$-10m^7n^8$$, 3) $$16a^{10}b^2$$