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