(-a)^3*(-2ab^2)^3-4ab^2*(7a^5b^4-1/2ab^3-5)=-a^3*(-8a^3b^6)-28a^6b^6+2a^2b^5+20ab^2=8a^6b^6-28a^6b^6+2a^2b^5+20ab^2=-20a^6b^6+2a^2b^5+20ab^2
