原式=[2/3(y-x)^n]×[2/5(y-x)^4n]×[1/3)(y-x)^2n]
=(2/3×2/5×1/3)×[(y-x)^n×(y-x)^4n×(y-x)^2n]
=4/45(y-x)^(n+4n+2n)
=4/45(y-x)^7n