Giải phương trình:
a/ \(\dfrac{x+1}{x^2+x+1}\) - \(\dfrac{x-1}{x^2-x+1}\) = \(\dfrac{3}{x\left(x^4+x^2+1\right)}\)
b/ \(\dfrac{9-x}{2009}\) + \(\dfrac{11-x}{2011}\) = 2
c/ \(\dfrac{15-x}{2010}\) + \(\dfrac{17-x}{2012}\) + \(\dfrac{19-x}{2014}\) = 3
d/ \(\dfrac{x-2014}{2007}\) + \(\dfrac{x-2012}{2009}\) + \(\dfrac{x-10}{2011}\) = \(\dfrac{x-2017}{2014}\) + \(\dfrac{x-2009}{2012}\) + \(\dfrac{x-2011}{2010}\)