Hi, Before I post my question, let me admit that my foundation on mathematics is poor. I am trying to work on it, specifically on the application part. When I came through the following image, I was stuck to understand why I will need one like Taylor's series in a simple case like "F+ΔF = F (x* + Δx)"? Why don't we live with F (x* + Δx) instead of expanding it as a series? What exactly is the benefit? Thanks.