1. The problem statement, all variables and given/known data I going thorough some of my old notes and I saw this question for a proof. If f is linear function but not a direct variation and not the constant function 0, then for every pair of real numbers a and c f(a + c) not equal to f(a)+f(c). 2. Relevant equations y = mx ( a linear function ) m = y/x 3. The attempt at a solution I can't seem to get the logic together, a linear function that is actually a direct variation produces contant distances on a number line, so i would think a function that isnt a direct variation would be map irregular dstances. I would like some direction as to how connect this the fact that additive distribution doesn't hold for such functions. thanks edit: I meant this for the precal section.