To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $\left(2x-5y\right)\left(2x+5y\right)$ and $2x+5y$ is $\left(2x-5y\right)\left(2x+5y\right)$. Multiply $\frac{2x-5y}{2x+5y}$ times $\frac{2x-5y}{2x-5y}$.
Since $\frac{4x^{2}+25y^{2}}{\left(2x-5y\right)\left(2x+5y\right)}$ and $\frac{\left(2x-5y\right)\left(2x-5y\right)}{\left(2x-5y\right)\left(2x+5y\right)}$ 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 $\left(2x-5y\right)\left(2x+5y\right)$ and $2x+5y$ is $\left(2x-5y\right)\left(2x+5y\right)$. Multiply $\frac{2x-5y}{2x+5y}$ times $\frac{2x-5y}{2x-5y}$.
Since $\frac{4x^{2}+25y^{2}}{\left(2x-5y\right)\left(2x+5y\right)}$ and $\frac{\left(2x-5y\right)\left(2x-5y\right)}{\left(2x-5y\right)\left(2x+5y\right)}$ have the same denominator, subtract them by subtracting their numerators.