To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $y\left(x-y\right)$ and $x\left(x-y\right)$ is $xy\left(x-y\right)$. Multiply $\frac{x}{y\left(x-y\right)}$ times $\frac{x}{x}$. Multiply $\frac{y}{x\left(x-y\right)}$ times $\frac{y}{y}$.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $y\left(x-y\right)$ and $x\left(x-y\right)$ is $xy\left(x-y\right)$. Multiply $\frac{x}{y\left(x-y\right)}$ times $\frac{x}{x}$. Multiply $\frac{y}{x\left(x-y\right)}$ times $\frac{y}{y}$.
