(18x^5-72x^3y^2)/(12x^3y^2-48x^2y^3+48xy^4)=18x^3(x^2-4y^2)/12xy^2*(x^2-4xy+4y^2)=3x^2(x-2y)*(x+2y)/2y^2(x-2y)^2=3x^2*(x+2y)/2y^2*(x-2y)
(72a^2bc^3-96a^4bc^2+32a^6bc)/(16a^5b^2c^3-36ab^2c^5)=8a^2bc(9c^2-12a^2c+4a^4)/4ab^2c^3(4a^4-9c^2)=2a(3c-2a^2)^2/bc^2(2a^2-3c)(2a^2+3c)= 2a(3c-2a^2)/bc^2(2a^2+3c)