（x-y）（x平方+3xy+y平方）-5xy（x-y）
=x³-x²y+3x²y-3xy²+xy²-y³-5x²y+5xy²
=x³-3x²y+3xy²-y³
=(x-y)³ x=6.61y=-3.39
=[6.61-(-3.39)]³
=(6.61+3.39)³
=10³
=1000