解
原式
=(x-y)(x-y)²(x-y)的5次方
=(x-y)的3次方×(x-y)的5次方
=(x-y)的8次方
=3的n次方×(-3²)×3的n+2次方
=-3的n+2次方×3的n+2次方
=-3的2n+4次方