原式=[(x-y)/x]^2n×[x/(y-x)]^2n+1,^2n是2n次幂,^2n+1是2n+1次幂
=[(y-x)/x]^2n×[x/(y-x)]^2n×[x/(y-x)]
=﹛[(y-x)/x]×[x/(y-x)]﹜^2n×[x/(y-x)]
=1^2n×[x/(y-x)]
=x/(y-x)