x+5/2009 + x+4/2010 = x+3/2011 + x+2/2012
=> 1 + x+5/2009 + 1 + x+4/2000 = 1 + x+3/2011 + 1 + x+2/2012
=> x+2014/2009 + x+2014/2000 = x+2004/2011 + x+2014/2012
=> x+2014/2009 + x+2014/2000 - x+2014/2011 - x+2014/2012 = 0
=> (x+2014).(1/2009 + 1/2010 - 1/2011 - 1/2012) = 0
Do 1/2009 > 1/2011; 1/2010 > 1/2012
=> 1/2009 + 1/2010 - 1/2011 - 1/2012 khác 0
=> x + 2014 = 0
=> x = -2014
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