Welcome. I am trying to solve numerical integration using Trapezoidal rule. I have two points a and b that I know their f(a) and f(b), respectively. Know suppose that I have a third point c having f(c). How can I determine the value of f(c), giving that I know c? Please notice that I don't know f(x), I have only straight lines on a graph.
I have tried the following formula, but was not succeeded:
f(c) = f(a) + ((c - a) / (b - a))