1、解:(1)(a+b)³
=(a+b) ²(a+b)
=(a²十2ab+b²)(a+b)
=a³+3a²b+3ab²+b³
(2)(x-5)³ =(x-5)²(x-5)-(x²-10x+25) (x-5) =x³- 5x²-10x2+50x-+25x -125 =x3-5x²+75x-125.
2、解:(a-b-c) ²=(a-b) ²-2(a-b)•c+C²
=a²-2ab+b²-2ac+2bc+c²
=a²+b²+c²-2ab-2ac+2bc.