a)
\(\dfrac{1}{x-1}+\dfrac{1}{x^2+x+1}=\dfrac{1}{x^3-1}\)
\(\Leftrightarrow\dfrac{x^2+x+1}{\left(x-1\right)\left(x^2+x+1\right)}+\dfrac{x-1}{\left(x-1\right)\left(x^2+x+1\right)}=\dfrac{1}{\left(x-1\right)\left(x^2+x+1\right)}\)
\(\Leftrightarrow x^2+x+1+x-1=1\)
\(\Leftrightarrow x^2+2x=1\)
Đến đây ko giải đc nữa =))