(x-y)^3n
=[(x-y)^3]^n
=[-(y-x)^3]^n
所以
n是奇数,原式=-(y-x)^3n*(y-x)^2n/(y-x)^5n
=-(y-x)^5n/(y-x)^5n
=-1
n是偶数,原式=(y-x)^3n*(y-x)^2n/(y-x)^5n
=(y-x)^5n/(y-x)^5n
=1
(x-y)^3n
=[(x-y)^3]^n
=[-(y-x)^3]^n
所以
n是奇数,原式=-(y-x)^3n*(y-x)^2n/(y-x)^5n
=-(y-x)^5n/(y-x)^5n
=-1
n是偶数,原式=(y-x)^3n*(y-x)^2n/(y-x)^5n
=(y-x)^5n/(y-x)^5n
=1