8) $$10a^5 - 7a^3 - (-a^5 + 6a²-8a^3) + a^2 = 10a^5 - 7a^3 + a^5 - 6a^2 + 8a^3 + a^2 = 11a^5 + a^3 - 5a^2$$
Ответ: $$11a^5 + a^3 - 5a^2$$