How to find the derivative of the loss function?

Question

Neural networks

Good day, there is the following task from the site "stepik " : https://stepik.org/lesson/261086/step/2?unit=241830 learning algebraic concepts, after a week of futile attempts, hands begin to fall . I ask for a little hint what is wrong in my formula, and, if not difficult, some reference materials on the topic of taking the derivative of functions I almost forgot, the result of doing all this is good: bound method EvalfMixin.evalf of (w*x*(-y*exp(-b - w*x) - y + 1) + (y*log(1/(exp(-b - w*x) + 1)) - (y - 1)*log(1/(exp(b + w*x) + 1)))*(exp(-b - w*x) + 1))/(w**2*(exp( -b - w*x) + 1))