I have a technical question that can simply be stated, "Is it possible to take the derivative of something that is not a function?"
I am aware that given an equation, one can still determine some form of piecewise solution or answer in terms of other variables that would provide an output for the slope at a given point on the original non-function; however, I'm not asking if this is possible. My question is simply, given that the definition of the derivative of f(x) is " f'(x)= lim(h->0) (f(x+h)-f(x))/h " is it technically possible to differentiate anything that is not a function (ie not passing vertical line test).
I am aware that given an equation, one can still determine some form of piecewise solution or answer in terms of other variables that would provide an output for the slope at a given point on the original non-function; however, I'm not asking if this is possible. My question is simply, given that the definition of the derivative of f(x) is " f'(x)= lim(h->0) (f(x+h)-f(x))/h " is it technically possible to differentiate anything that is not a function (ie not passing vertical line test).