The derivative of a function of a real variable measures the sensitivity to change of the function value (output value)—with respect to a change in its argument (input value). Derivatives are a fundamental tool of calculus. For example, the derivative of the position of a moving object with respect to time is the object's velocity: this measures how quickly the position of the object changes when time advances.

In calculus, the quotient rule is a method of finding the derivative of a function that is the ratio of two differentiable functions. Let f(x)=g(x)/h(x), where both g and h are differentiable and h(x)≠0. The quotient rule states that the derivative of f(x) is fʼ(x)=(gʼ(x)h(x)-g(x)hʼ(x))/[h(x)]².