| $$ \begin{aligned}\frac{y^2+9y+20}{y^2-16}& \xlongequal{ \color{blue}{ \text{\normalsize{ \htmlClass{explanationCircle explanationCircle1}{\textcircled {1}} } }}}\frac{y+5}{y-4}\end{aligned} $$ | |
| ① | Simplify $ \dfrac{y^2+9y+20}{y^2-16} $ to $ \dfrac{y+5}{y-4} $. Factor both the denominator and the numerator, then cancel the common factor. $\color{blue}{y+4}$. $$ \begin{aligned} \frac{y^2+9y+20}{y^2-16} & =\frac{ \left( y+5 \right) \cdot \color{blue}{ \left( y+4 \right) }}{ \left( y-4 \right) \cdot \color{blue}{ \left( y+4 \right) }} = \\[1ex] &= \frac{y+5}{y-4} \end{aligned} $$ |