(a-2+b)(a+2+b)
=(a+b)^2-2^2
=a^2+b^2+2ab-4
(x^5y^3-2x^y^2+3/4x^2y^2)/1/12x^2y^2
=(x^5y^3-5x^2y^2/4)*12/x^2y^2
=x^2y^2(x^3y-5/4)*12/x^2y^2
=12x^3y-15