Question

[Trần Tuệ Nhi]

so sanh :A=2007 x 2009             B=2008 x 2008

A= 2006 x 2010                   B=2008 x2008

Answer 1

[Edogawa Conan]

+) Ta có:

A = 2007 x 2009 = 2007 x 2008 + 2007 

B = 2008 x 2008 = 2007 x 2008 + 2008

Do 2007 < 2008 => 2007 x 2008 + 2007 < 2007 x 2008 + 2008

=> A < B

+) Ta có: 

A = 2006 x 2010 = 2006 x 2008 + 2006 x 2

B = 2008 x 2008 = 2008 x 2006 + 2008 x 2

Do 2006 x 2 < 2008 x 2 => 2006 x 2008 + 2006 x 2 < 2008 x 2006 + 2008 x 2

=> A < B

Answer 2

[Vũ Văn Huy]

B=2008 x 2008 = (2007+1) x (2009-1)=2007 x 2009 +2009-2007-1=2007 x 2009+1 >A=2007 x 2009

B=2008 x 2008 = (2006+2) x (2010-2)=2007 x 2009 +2009 x 2-2007 x 2-4=2007 x 2009+4 >A=2006 x 2010