TITLE: Is constant function also a linear function?
QUESTION [5 upvotes]: Is a function of the form $F (x) = C$, for some $C \in \mathbb R$, a linear function?  If no, what about its graph? Isn't it a line?
Please elaborate on the answer.
Thank you very much.

REPLY [2 votes]: For $C=0$, $F$ is a linear function. For $C\neq 0$, $F$ is an affine-linear function, but not a linear function.
However, in school mathematics, the term "linear" is often also used for affine-linear functions.
So the answer to your question is: It depends on your definition for "linear".