(1)a³+b³
=a³+a²b-a²b+b³
=a²(a+b)-b(a²-b²)
=a²(a+b)-b(a+b)(a-b)
=(a+b)[a²-b(a-b)]
=(a+b)(a²-ab+b²)
(2)a³-b³
=a³-a²b+a²b-b³
=a²(a-b)+b(a²-b²)
=a²(a-b)+b(a+b)(a-b)
=(a-b)[a²+b(a+b)]
=(a-b)(a²+ab+b²)
(3)(a-b)³
=(a-b)(a-b)²
=(a-b)(a²-2ab+b²)
=a³-3a²b+3ab²-b³