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