I read a few posts about the matter but they seemed to contradict each other. So what are the differences between a function and an equation? Furthermore; what explains the fact the some of them are graphed the same even though they are not the same? I get that functions are defined as mappings from one set to another with the restriction that one input must only map to one output. But then what are equations? One of the explanations I read was that functions output a value for every input and equations only show the relationship between variables. But then the examples confused me because "f(x) = x" was said to be a function and "x - y = 0" was said to be an equation. But can't "x - y = 0" be viewed as the function of x and y such that any input outputs zero? I mean, there are such things as constant functions, right?