x^2*x^8+x^13/x^3 =2x^10
a^19/(a^12/a^3)=1
(x-2y)^5/(2y-x)^3=-(x-2y)^2
(x-y)^5/(x-y) =(x-y)^4
(x-y)^6/(y-x)^4=(x-y)^2
(x-2y)^6/(2y-x)^3=(2y-x)^3