To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $a+y$ and $\left(y+a\right)\left(-y+a\right)$ is $\left(y+a\right)\left(-y+a\right)$. Multiply $\frac{a-2y}{a+y}$ times $\frac{-y+a}{-y+a}$.
Since $\frac{\left(a-2y\right)\left(-y+a\right)}{\left(y+a\right)\left(-y+a\right)}$ and $\frac{y^{2}-5ay}{\left(y+a\right)\left(-y+a\right)}$ 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 $a+y$ and $\left(y+a\right)\left(-y+a\right)$ is $\left(y+a\right)\left(-y+a\right)$. Multiply $\frac{a-2y}{a+y}$ times $\frac{-y+a}{-y+a}$.
Since $\frac{\left(a-2y\right)\left(-y+a\right)}{\left(y+a\right)\left(-y+a\right)}$ and $\frac{y^{2}-5ay}{\left(y+a\right)\left(-y+a\right)}$ have the same denominator, subtract them by subtracting their numerators.