請問這條數怎樣做???

(a+b)(b+c)(c+a)
=acc+abb+baa+bcc+cbb+caa+2abc
=a(cc+bb)+b(aa+cc)+c(aa+cc)+2abc
>=a(2bc)+b(2ac)+c(2ab)+2abc
=8abc

2007-07-05 12:59:58 補充：
(x-y)^2 =0xx-2xy yy =0xx yy =2xyput x=a,y=baa bb =2absimularly,bb cc =2bc aa cc =2ac

2007-07-05 13:02:59 補充：
佢只係話正數,所以可以係0.3, 0.幾咁,最細唔係1

設a,b,c最細都係1~
left hand side:(1+1)(1+1)(1+1)
=2*2*2
=8
right hand side:8(1)(1)(1)
=8
最細都等於8~所以(a+b)(b+c)(c+a)>=8abc