[(3a^2b-2ab^2)(4a^2-ab^2)-(2ab^2)^2]÷(-1/2a^2b^2)
=(12a^4b-3a^3b^3-8a^3b^2+2a^2b^4-4a^2b^4)÷(-1/2a^2b^2)
=(12a^4b-3a^3b^3-8a^3b^2-2a^2b^4)÷(-1/2a^2b^2)
=-24a^2+6ab+16a+4b^2