To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $3\left(x+1\right)$ and $6\left(x-1\right)$ is $6\left(x-1\right)\left(x+1\right)$. Multiply $\frac{x-1}{3\left(x+1\right)}$ times $\frac{2\left(x-1\right)}{2\left(x-1\right)}$. Multiply $\frac{x-2}{6\left(x-1\right)}$ times $\frac{x+1}{x+1}$.
Since $\frac{\left(x-1\right)\times 2\left(x-1\right)}{6\left(x-1\right)\left(x+1\right)}$ and $\frac{\left(x-2\right)\left(x+1\right)}{6\left(x-1\right)\left(x+1\right)}$ have the same denominator, subtract them by subtracting their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $6\left(x-1\right)\left(x+1\right)$ and $9\left(x-1\right)\left(x+1\right)$ is $18\left(x-1\right)\left(x+1\right)$. Multiply $\frac{x^{2}-3x+4}{6\left(x-1\right)\left(x+1\right)}$ times $\frac{3}{3}$. Multiply $\frac{x^{2}+2x-6}{9\left(x-1\right)\left(x+1\right)}$ times $\frac{2}{2}$.
Since $\frac{3\left(x^{2}-3x+4\right)}{18\left(x-1\right)\left(x+1\right)}$ and $\frac{2\left(x^{2}+2x-6\right)}{18\left(x-1\right)\left(x+1\right)}$ 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 $3\left(x+1\right)$ and $6\left(x-1\right)$ is $6\left(x-1\right)\left(x+1\right)$. Multiply $\frac{x-1}{3\left(x+1\right)}$ times $\frac{2\left(x-1\right)}{2\left(x-1\right)}$. Multiply $\frac{x-2}{6\left(x-1\right)}$ times $\frac{x+1}{x+1}$.
Since $\frac{\left(x-1\right)\times 2\left(x-1\right)}{6\left(x-1\right)\left(x+1\right)}$ and $\frac{\left(x-2\right)\left(x+1\right)}{6\left(x-1\right)\left(x+1\right)}$ have the same denominator, subtract them by subtracting their numerators.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $6\left(x-1\right)\left(x+1\right)$ and $9\left(x-1\right)\left(x+1\right)$ is $18\left(x-1\right)\left(x+1\right)$. Multiply $\frac{x^{2}-3x+4}{6\left(x-1\right)\left(x+1\right)}$ times $\frac{3}{3}$. Multiply $\frac{x^{2}+2x-6}{9\left(x-1\right)\left(x+1\right)}$ times $\frac{2}{2}$.
Since $\frac{3\left(x^{2}-3x+4\right)}{18\left(x-1\right)\left(x+1\right)}$ and $\frac{2\left(x^{2}+2x-6\right)}{18\left(x-1\right)\left(x+1\right)}$ have the same denominator, add them by adding their numerators.