you have studied limits, how \(\Delta x\) turns into \(dx\). Now it is time to apply this. It is time to learn Differentiation, AKA derivatives. The man himself, Issac Newton, wanted to find the velocity function, knowing only the distance function, but how, after all, velocity is the slope of the line between 2 positions, where the y axis is the time, so he thought of the brilliant idea. Why not use those limits to get the velocity function. lets think of it like this, u want to get the slope of 2 points, well that is: $$\frac{y_2-y_1}{x_2-x_1}$$ AKA $$\frac{f(x_2)-f(x_1)}{x_2-x_1}$$ lets asume that \(x_1 = x\) and \(x_2 = x+h\) where h is the amount of increase in x $$\frac{f(x+h)-f(x)}{x+h-x}$$ simplifying to: $$\frac{f(x+h)-f(x)}{h}$$ now lets use limits to make them approach 1 point: $$\lim_{h \to 0}\frac{f(x+h)-f(x)}{h}$$ this is the standard formula for any derivative, however, this formula might be abit to difficult to apply in complicated problems, so there are may rules that have been created over the years, for example: $$\frac{d}{dx} c = 0$$