For any value of \(c\), where \(c\in \mathbb {R}\), if \(f(x)\) is the constant function given by \(f(x)=c\), then \(\frac {df}{dx}=0\).
This is one of the rules of Differentiation.
Bibliography
“Differentiation Rules.” 2022. Wikipedia, December. https://en.wikipedia.org/w/index.php?title=Differentiation_rules&oldid=1129937443.