To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $x-y$ and $y-x$ is $-x+y$. Multiply $\frac{x^{2}+y^{2}}{x-y}$ times $\frac{-1}{-1}$.
To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $x-y$ and $y-x$ is $-x+y$. Multiply $\frac{x^{2}+y^{2}}{x-y}$ times $\frac{-1}{-1}$.
