To check Example $4,$ Kara graphs
$$
y_{1}=\frac{7 x^{2}+21 x}{14 x} \text { and } y_{2}=\frac{x+3}{2}
$$
since the graphs of $y_{1}$ and $y_{2}$ appear to be identical, Kara believes that the domains of the functions described by $y_{1}$ and $y_{2}$ are the same, $\mathbb{R} .$ How could you convince Kara otherwise?