Resposta :
[tex]\Large\boxed{\begin{array}{l}\sf f(x)=3\sqrt{x-4}\\\sf x-4\geqslant 0\\\sf x\geqslant4\\\sf df(x)=[4,\infty[\end{array}}[/tex]
[tex]\Large\boxed{\begin{array}{l}\sf f(x)=3\sqrt{x-4}\\\sf x-4\geqslant 0\\\sf x\geqslant4\\\sf df(x)=[4,\infty[\end{array}}[/tex]