①（2ax）^2·（-3/4a^4x^3y^3）÷（-1/2a^5xy^2）=(-3a^6x^5y^3）÷（-1/2a^5xy^2）=6ax^4y②(21a^3-14a^2+7a)÷7a=3a^2-2a+1③（24m^3n-16m^2n^2+mn^3）÷(-8m)=-3m^2n+2mn^2-1/8n^2④(36x^6-24x^4+12x^3)÷12x^2=...