I am assigned a two-part question. The first part (a.) asks to describe the method for finding the steepest incline from a point and travelling in that direction and repeating the process to find a function's minimum or maximum. The answer is the process of determining the gradient of the function. Part (b.) is the part of the question that I need help with.

Suppose we have function f with continuous partial derivatives, but we are not able to calculate them. How can we modify the process in part (a) so that it can still work? (How could we determine in which direction f has a steepest decline without the partial derivatives?)