由于x/y=8,x＝8y且Y不等于0,
（x^2-3xy+2y^2）/（x^2-5xy+4y^2）
＝(X-Y)(X-2Y)/(X-Y)(X-4Y)
=(X-2Y)/(X-4Y)
所以上式为
(8Y-2Y)/(8Y-4Y)=6/4=3/2=1.5