(x^2-3XY+2Y^2)/(X^2-2XY+Y^2)=(x-2y)(x-y)/(x-y)^2=(x-2y)/(x-y)=(x-y-y)/(x-y)=1- y/(x-y)=1- 1/(x/y -1)=1- 1/(2/7 -7/7)=1+ 1/(5/7)=1+ 7/5=12/5
