To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $x-1$ and $\left(x-1\right)\left(-x^{2}-x-1\right)$ is $\left(x-1\right)\left(-x^{2}-x-1\right)$. Multiply $\frac{2x}{x-1}$ times $\frac{-x^{2}-x-1}{-x^{2}-x-1}$.
Since $\frac{2x\left(-x^{2}-x-1\right)}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ and $\frac{2x^{3}+2x^{2}}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ have the same denominator, add them by adding their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x-1\right)\left(-x^{2}-x-1\right)$ and $x^{2}+x+1$ is $\left(x-1\right)\left(x^{2}+x+1\right)$. Multiply $\frac{-2x}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ times $\frac{-1}{-1}$. Multiply $\frac{1}{x^{2}+x+1}$ times $\frac{x-1}{x-1}$.
Since $\frac{-\left(-2\right)x}{\left(x-1\right)\left(x^{2}+x+1\right)}$ and $\frac{x-1}{\left(x-1\right)\left(x^{2}+x+1\right)}$ have the same denominator, add them by adding their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $x-1$ and $\left(x-1\right)\left(-x^{2}-x-1\right)$ is $\left(x-1\right)\left(-x^{2}-x-1\right)$. Multiply $\frac{2x}{x-1}$ times $\frac{-x^{2}-x-1}{-x^{2}-x-1}$.
Since $\frac{2x\left(-x^{2}-x-1\right)}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ and $\frac{2x^{3}+2x^{2}}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ have the same denominator, add them by adding their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(x-1\right)\left(-x^{2}-x-1\right)$ and $x^{2}+x+1$ is $\left(x-1\right)\left(x^{2}+x+1\right)$. Multiply $\frac{-2x}{\left(x-1\right)\left(-x^{2}-x-1\right)}$ times $\frac{-1}{-1}$. Multiply $\frac{1}{x^{2}+x+1}$ times $\frac{x-1}{x-1}$.
Since $\frac{-\left(-2\right)x}{\left(x-1\right)\left(x^{2}+x+1\right)}$ and $\frac{x-1}{\left(x-1\right)\left(x^{2}+x+1\right)}$ have the same denominator, add them by adding their numerators.