For a cubic function $$y=f(x)$$ three points A, B and C lie on a straight line with respective coordinates (-p,f(p)),(0,f(0)) and (p,f(p)) where p is a non zero constant.
a. Show that $$\frac{f(-p)+f(p)}{2} =f(0)$$
I tried
$$\frac{f(-p)+f(p)}{2} =\frac{0}{2} = 0 = f(0)$$
That doesn't seem...