(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