[tex] \bf{r(x) = 7 }[/tex]

[tex] \bf{r(x) = \frac{d}{dx} \: (7)}[/tex]

[tex] \large \bf {{ \purple{ \boxed{\pink{ \boxed{\orange{\boxed{ \blue{ \boxed{ \red{ \boxed{\color{lime}{r(x) = 0}}}}}}}}}}}}}[/tex]