Giải thích các bước giải:
$\dfrac{3-x}{2009}-\dfrac{2-x}{2010}+\dfrac{1-x}{2011}=-1$
$\to (1+\dfrac{3-x}{2009})-(1+\dfrac{2-x}{2010})+(1+\dfrac{1-x}{2011})=0$
$\to \dfrac{2009+3-x}{2009}-\dfrac{2010+2-x}{2010}+\dfrac{2011+1-x}{2011}=0$
$\to \dfrac{2012-x}{2009}-\dfrac{2012-x}{2010}+\dfrac{2012-x}{2011}=0$
$\to (2012-x)(\dfrac{1}{2009}-\dfrac{1}{2010}+\dfrac{1}{2011})=0$
$\to x=2012$
