To add or subtract expressions, expand them to make their denominators the same. Least common multiple of $a\left(a+1\right)$ and $\left(a-2\right)\left(a+1\right)$ is $a\left(a-2\right)\left(a+1\right)$. Multiply $\frac{a+2}{a\left(a+1\right)}$ times $\frac{a-2}{a-2}$. Multiply $\frac{3}{\left(a-2\right)\left(a+1\right)}$ times $\frac{a}{a}$.
Since $\frac{\left(a+2\right)\left(a-2\right)}{a\left(a-2\right)\left(a+1\right)}$ and $\frac{3a}{a\left(a-2\right)\left(a+1\right)}$ 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 $a\left(a+1\right)$ and $\left(a-2\right)\left(a+1\right)$ is $a\left(a-2\right)\left(a+1\right)$. Multiply $\frac{a+2}{a\left(a+1\right)}$ times $\frac{a-2}{a-2}$. Multiply $\frac{3}{\left(a-2\right)\left(a+1\right)}$ times $\frac{a}{a}$.
Since $\frac{\left(a+2\right)\left(a-2\right)}{a\left(a-2\right)\left(a+1\right)}$ and $\frac{3a}{a\left(a-2\right)\left(a+1\right)}$ have the same denominator, subtract them by subtracting their numerators.
