Add $ \dfrac{x}{x^2+x-2} $ and $ \dfrac{1}{x+2} $ to get $ \dfrac{ \color{purple}{ 2x-1 } }{ x^2+x-2 }$.

To add raitonal expressions, both fractions must have the same denominator.
We can create a common denominator by multiplying the second fraction by $\color{blue}{x-1}$.

$$ \begin{aligned} \frac{x}{x^2+x-2} + \frac{1}{x+2} & = \frac{ x }{ x^2+x-2 } + \frac{ 1 \cdot \color{blue}{ \left( x-1 \right) }}{ \left( x+2 \right) \cdot \color{blue}{ \left( x-1 \right) }} = \\[1ex] &=\frac{ \color{purple}{ x } }{ x^2+x-2 } + \frac{ \color{purple}{ x-1 } }{ x^2+x-2 }=\frac{ \color{purple}{ 2x-1 } }{ x^2+x-2 } \end{aligned} $$