The reciprocal rule or reciprocal value rule is used to derive mathematical functions of the form
If the function from an interval into the real or complex numbers is differentiable at the point with , then the function
at the point is also differentiable and according to the chain rule, the following applies for the derivative:
The reciprocal rule is as follows in short form:
The reciprocal rule can also be a special case of the quotient rule to be interpreted.
example
The derivative of the function
is calculated at all points where is according to the above reciprocal rule