Ta thấy :A = 1+2012+20122+20123+...+201272
=> 2012A = (1+2012+20122+20123+...+201272)*2012
=> 2012A = 2012+20122+20123+20124+...+201272+20122013
=> 2012A = (1+2012+20122+20123+...+201272)+201273-1
=> 2012A = A+201273-1
=> 2011A = 201273-1
=> A = (201273-1) : 2011
Mà [(201273-1) : 2011] < (201273-1)
=> A < B
2012A = (1+2012+20122+20123+...+201272).2012
=> 2012A = 2012+20122+20123+20124+...+201272+20122013
=> 2012A = (1+2012+20122+20123+...+201272)+201273-1
=> 2012A = A+201273-1
=> 2011A = 201273-1
=> A = (201273-1) : 2011
Mà [(201273-1) : 2011] < (201273-1)
=> A < B
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