數學知識交流 － 代數式(數論)難題 (2)

(1) (a+b)+k = ab => k = ab – a – b(2) ab+(a+b)<2k=>ab+(a+b)<2(ab – a – b)=>0 < ab – 3a – 3b=>9 < ab – 3a – 3b+9=(a – 3)(b – 3)因此(a – 3)及(b – 3)必須為同時大於或小於0即a,b同時大於3或同時小於3

2011-12-20 19:49:04 補充：
(a-3)(b-3)>9
當a>3時b>3+9/(a-3)
當a<3時b<3+9/(a-3)

2011-12-20 21:33:04 補充：
a and b can never be = 3.
The graphical representation of the probable values are as shown (x-axis is a, y-axis is b):
http://i1090.photobucket.com/albums/i376/Nelson_Yu/int-2126.jpg

2011-12-20 21:34:46 補充：
I do not see -3 <= a <= 3 is a meaningful range...