(1)(a+b)(a 2﹣ab+b 2)=a 3+b 3;(a﹣b)(a 2+ab+b 2)=a 3﹣b 3;
(2)(﹣x﹣2y)(x 2﹣2xy+4y 2)=(﹣x) 3+(﹣2y) 3=﹣x 3﹣8y 3.