The derivative of cos x is -sin x-formula-solution.html). This means that the rate of change of the cosine function at any point is equal to the negative of the sine function at that point. The derivative of a function characterizes the rate of change of the function at some point, and the process of finding the derivative is called differentiation. The derivative of cos x can be calculated using different methods, such as the definition of the limit, chain rule, and Eulers complex representation of trigonometric functions-formula-solution.html).