(a^2+3)(a-2)-a(a^2-2a-2)
=a^3-2a^2+3a-2-a^2+2a^2+2a
=5a-2
(3/5a^5b^3+9/5a^7b^4-9/2a^5b^5)除以3/4a^5b^3)
=4/5+12/5a^2b-6b^2